Xanthenyl cubane analogs with activity at the metabotropic glutamate receptors

ABSTRACT

The present invention relates to therapeutically active cubane compounds, a method of preparing the same, and to pharmaceutical compositions comprising the compounds. The novel compounds are useful in treating and preventing diseases of the central nervous system related to the metabotropic glutamate receptor system.

FIELD OF THE INVENTION

This invention pertains to therapeutically active cubane derivatives, amethod for preparing the same, pharmaceutical compositions comprisingthe compounds and a method of preventing and treating diseasesassociated with one or more metabotropic glutamate receptors.

BACKGROUND OF THE INVENTION

The acidic amino acid L-Glutamate is recognized as the major excitatoryneurotransmitter in the CNS. The receptors that respond to L-Glutamateare called excitatory amino acid receptors. The excitatory amino acidreceptors are thus of great physiological importance, playing a role ina variety of physiological processes, such as long-term potentiation(learning and memory), the development of synaptic plasticity, motorcontrol, respiratory and cardiovascular regulation, and sensoryperception.

Excitatory amino acid receptors are classified into two general typesand both are activated by L-Glutamic acid and its analogs. Receptorsactivated by L-Glutamic acid that are directly coupled to the opening ofcation channels in the cell membrane of the neurons are termed“ionotropic.” This type of receptor has been subdivided into at leastthree subtypes, which are defined by the depolarizing actions of theselective agonists N-Methyl-D-aspartate (NMDA),α-Amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA), and Kainicacid (KA).

The second general type of receptor is the G-protein or secondmessenger-linked “metabotropic” excitatory amino acid receptor. Thissecond type is coupled to multiple second messenger systems that lead toenhanced phosphoinositide hydrolysis, activation of phospholipase D,increases or decreases in cAMP formation, and changes in ion channelfunction (Schoepp and Conn, Trends in Pharmacological Science, 14:13,1993). Both types of receptors appear not only to mediate normalsynaptic transmission along excitatory pathways but also to participatein the modification of synaptic connections during development andthroughout life.

So far eight different clones of the G-protein-coupled metabotropicglutamate receptors (mGluRs) have been identified (Knopfel et al., 1995,J. Med. Chem., 38, 1417-1426). These receptors function to modulate thepresynaptic release of L-Glutamate, and the postsynaptic sensitivity ofthe neuronal cell to L-Glutamate excitation. Based on pharmacology,sequence homology and the signal transduction pathway that theyactivate, the mGluRs have been subclassified into three groups. ThemGluR1 and mGluR5 receptors form group I. They are coupled to hydrolysisof phosphatidylinositol (PI) and are selectively activated by(RS)-3,5-dihydroxyphenylglycine (Brabet et al., Neuropharmacology, 34,895-903, 1995). Group II comprises mGluR₂ and mGluR₃ receptors. They arenegatively coupled to adenylate cyclase and are selectively activated by(2S,1′R,2′R,3′R)-2-(2,3-dicarboxycyclopropyl)glycine (DCG-IV; Hayashi etal., Nature, 366, 687-690, 1993). Finally, the mGluR₄, mGluR₆, mGluR₇and mGluR₈ receptors belong to group III. They are also negativelycoupled to adenylate cyclase and are selectively activated by(L)-2-amino-4-phosphonobutyric acid (L-AP4; Knopfel et al., 1995, J.Med. Chem., 38, 1417-1426).

Agonists and antagonists of these receptors are useful for the treatmentof acute and chronic neurodegenerative conditions, and as antipsychotic,anticonvulsant, analgesic, anxiolytic, antidepressant, and anti-emeticagents. Antagonists and agonists of neural receptors are classified asselective for a particular receptor or receptor subtype, or asnon-selective. Antagonists may also be classified as competitive ornon-competitive. While competitive and non-competitive antagonists acton the receptors in a different manner to produce similar results,selectivity is based upon the observations that some antagonists exhibithigh levels of activity at a single receptor type, and little or noactivity at other receptors. In the case of receptor-specific diseasesand conditions, the selective agonists and antagonists are of the mostvalue.

Compounds such as L-Glutamic acid, Quisqualic acid and Ibotenic acid areknown to act as non-selective agonists on the mGluRs, while selectiveionotropic glutamate receptor agonists such as NMDA, AMPA and Kainicacid have little effect on these receptors. Recently a few compoundswithout activity at the ionotropic glutamate receptors but with activityat the metabotropic receptors have been identified. These includetrans-ACPD (trans (1S,3R-1-aminocyclopentane-1,3-dicarboxylic acid), thepartial agonist L-AP3 (L-2-amino-3-phosphonopropionic acid; Palmer, E.,Monaghan, D. T. and Cotman, C. W. Eur. J. Pharmacol. 166, 585-587, 1989;Desai, M. A. and Conn, P. J. Neuroscience Lett. 109, 157-162, 1990;Schoepp, D. D. et al., J. Neurochemistry. 56, 1789-1796, 1991; SchoeppD. D. and Johnson B. G. J. Neurochemistry 53, 1865-1613, 1989), L-AP4(L-2-amino-4-phosphonobutyric acid) which is an agonist at the mGluR₄receptor (Thomsen C. et al., Eur. J. Pharmacol. 227, 361-362, 1992) andsome of the isomers of CCG (2-(carboxycyclopropyl)glycines) especiallyL-CCG-I and L-CCG-II (Hayashi, Y. et al., Br. J. Pharmacol. 107,539-543, 1992).

Very few selective antagonists at the mGluRs have been reported. Howeversome phenylglycine derivatives, S-4CPG (S-4-carboxyphenylglycine),S-4C3HPG (S-4-carboxy -3-hydroxyphenylglycine) and S-MCPG(S-α-methyl-4-carboxyphenylglycine) have been reported to antagonizetrans-ACPD-stimulated phosphoinositide hydrolysis and thus possibly actas antagonists at mGluR₁ and mGluR₅ subtypes (Thomsen, C. and Suzdak, P,Eur. J. Pharmacol. 245,299, 1993).

Research directed towards mGluRs is beginning to show that mGluRs may beimplicated in a number of normal as well as pathological mechanisms inthe brain an spinal cord. For example, activation of these receptors onneurons can: influence levels of alertness, attention and cognition;protect nerve cells from excitotoxic damage resulting from ischemia,hypoglycemia and anoxia; modulate the level of neuronal excitation;influence central mechanisms involved in controlling movement; reducesensitivity to pain; reduce levels of anxiety.

The use of compounds active at the mGluRs for the treatment of epilepsyis corroborated by investigations of the influence of trans-ACPD on theformation of convulsions (Sacaan and Schoepp, Neuroscience Lett. 139,77, 1992) and that phosphoinositide hydrolysis mediated via mGluR isincreased after kindling experiments in rats (Akiyama et al. Brain. Res.569, 71, 1992). Trans-ACPD has been shown to increase release ofdopamine in the rat brain, which indicates that compounds acting on themGluRs might be usable for the treatment of Parkinson's disease andHuntington's Chorea (Sacaan et al., J. Neurochemistry 59, 245, 1992).

Trans-ACPD has also been shown to be a neuroprotective agent in a medialcerebral artery occlusion (MCAO) model in mice (Chiamulera et al. Eur.J. Pharmacol. 215, 353, 1992), and it has been shown to inhibitNMDA-induced neurotoxicity in nerve cell cultures (Koh et al., Proc.Natl. Acad. Sci. USA 88, 9431, 1991). The mGluR-active compounds arealso implicated in the treatment of pain. This is proved by the factthat antagonists at the metabotropic glutamate receptors antagonizesensory synaptic response to noxious stimuli of thalamic neurons (Eaton,S. A. et al., Eur. J. Neuroscience, 5, 186, 1993).

The use of compounds active at the mGluRs for treatment of neurologicaldiseases such as senile dementia have also been indicated by thefindings of Zheng and Gallagher (Neuron 9, 163, 1992) and Bashir et al.(Nature 363, 347, 1993) who demonstrated that activation of mGluRs isnecessary for the induction of long-term potentiation (LTP) in nervecells (septal nucleus, hippocampus) and the finding that long-termdepression is induced after activation of metabotropic glutamatereceptors in cerebellar granule cells (Linden et al. Neuron 7, 81,1991).

Thus compounds that demonstrate either activating or inhibiting activityat mGluRs have therapeutic potential for the treatment of neurologicaldisorders. These compounds have application as new drugs to treat bothacute and chronic neurological disorders, such as stroke and headinjuries; epilepsy; movement disorders associated with Parkinson'sdisease and Huntington's chorea; pain; anxiety; AIDS dementia; andAlzheimer's disease. Since the mGluRs can influence levels of alertness,attention and cognition; protect nerve cells from excitotoxic damageresulting from ischemia, hypoglycemia and anoxia; modulate the level ofneuronal excitation; influence central mechanisms involved incontrolling movement; reduce sensitivity to pain; and reduce levels ofanxiety, these compounds can also be used to influence these situationsand also find use in learning and memory deficiencies such as seniledementia. mGluRs may also be involved in addictive behavior, alcoholism,drug addiction, sensitization and drug withdrawal (Science, 280:2045,1998), so compounds acting at mGluRs might also be used to treat thesedisorders.

The current pharmaceutical options for treating neurological disorderstend to be very general and non-specific in their actions in that,although they may reduce the clinical symptoms associated with aspecific neurological disorder, they may also negatively impact normalfunction of the central nervous system of patients. Thus new cellulartargets and drugs that are more specific in their actions require to beidentified and developed and thus a need remains for chemical compoundsthat demonstrate specific binding characteristics towards mGluRs.

SUMMARY OF THE INVENTION

It is an object of this invention to provide xanthenyl cubane analogswith activity at the metabotropic glutamate receptors. In accordancewith an aspect of the present invention there is provided a compound ofthe formula:

-   -   or a pharmaceutically acceptable salts thereof, or a        pharmaceutically acceptable metabolically-labile ester or amide        thereof, wherein:    -   R1 is an acidic group selected from the group of carboxyl,        phosphono, phosphino, sulfono, sulfino, borono, tetrazol,        isoxazol, —CH₂-carboxyl, —CH₂-phosphono, —CH₂-phosphino,        —CH₂-sulfono, —CH₂-sulfino, —CH₂-borono, —CH₂-tetrazol, and        —CH₂-isoxazol;    -   R2 is a basic group selected from the group of 1°amino, 2°        amino, 3°amino, quaternary ammonium salts, imidazol, guanidino,        boronoamino, allylurea, thiourea, and NHR5, wherein R5 is —H or        an acyl group;    -   R3 is of the formula;        -   wherein:            -   Y is absent or selected from the group of (CH₂)_(n)                (where n=1-4), C═O, O, or NH;            -   X is selected from the group of O, NH, S, S═O, or SO₂;            -   R_(a), R_(b), R_(c), R_(d), R_(e), R_(f), R_(g) and                R_(h) are independently selected from the group of —H,                hydroxyl, lower alkyl, substituted lower alkyl, lower                alkoxy, alkenyl, alkynyl, amino, halogen, aryl,                substituted aryl, nitrile, acyl, carboxy or amido;    -   R4 is a group selected from the group of carboxyl, phosphono,        phosphino, sulfono, sulfino, borono, tetrazol, isoxazol.

In accordance with another aspect of the invention there is provided aprocess for the preparation of the compounds of the present invention,or a pharmaceutically acceptable metabolically-labile ester or amidethereof, or a pharmaceutically acceptable salt thereof, which comprises:

-   -   (a) hydrolyzing a compound of formula:        -   wherein: R′1 is an acidic group selected from the group of            carboxyl, phosphono, phosphino, sulfono, sulfino, borono,            tetrazol, isoxazol, —CH₂-carboxyl, —CH₂-phosphono,            —CH₂-phosphino, —CH₂-sulfono, —CH₂-sulfino, —CH₂-borono,            —CH₂-tetrazol, —CH₂-isoxazol and higher analogues thereof,            or a protected form thereof, R3 is as defined above and R5            represents a hydrogen atom or an acyl group, and wherein            preferred values for R5 are hydrogen and (2-6C) alkanoyl            groups, such as acetyl; or    -   (b) deprotecting and hydrolyzing a compound of formula (II b)        -   wherein R′1 and R3 are as defined above; or    -   (c) hydrolyzing a compound of formula:        wherein: R6 and R7 each independently represent a hydrogen atom,        a (2-6C) alkanoyl group, a (1-4C) alkyl group, a (3-4C) alkenyl        group or a phenyl (1-4C) alkyl group in which the phenyl is        unsubstituted or substituted by halogen, (1-4C) alkyl or (1-4C)        alkoxy, or a salt thereof, R′1 and R3 are as defined above; or    -   (d) deprotecting a compound of formula:        -   wherein: R8 represents a hydrogen atom or a carboxyl            protecting group, or a salt thereof, and R9 represents a            hydrogen atom or a nitrogen protecting group, R′1 and R3 are            as defined above;    -   whereafter, if necessary and/or desired:        -   (i) resolving the compound of the present invention;        -   (ii) converting the compound of the present invention into a            non-toxic metabolically-labile ester or amide thereof;            and/or            converting the compound of the present invention or a            non-toxic metabolically-labile ester or amide thereof into a            pharmaceutically acceptable salt thereof.

In accordance with another aspect of the invention, there is providedthe use of a therapeutically effective amount of a compound having theformula:

or a substituted xanthene derivative thereof, or a pharmaceuticalcomposition comprising said compound and a pharmaceutically acceptablecarrier, in the treatment of a mammal in need of such therapy.

In accordance with another aspect of the invention, there is providedthe use of a prophylactically effective amount of a compound having theformula:

or a substituted xanthene-derivative thereof, or a pharmaceuticalcomposition comprising said compound and a pharmaceutically acceptablecarrier, as a neuroprotectant in a mammal in need of such therapy.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates the neuroprotective effects of one of the compounds(thioxanthenyl cubane) of the invention (compound 6) against anoxiainduced cell death. The dark bars represent % living cells while thelight bars represent % living cells 24 hours post anoxic insult in thepresence of the compound (a=control; b and c=different concentrations ofthe same thioxanthenyl compound)

FIG. 2 illustrates the neuroprotective effects of one of the compoundsof the invention (thioxanthenyl cubane, compound 6) in the rat globalischemia model. A: Normal brain tissue; B: brain tissue 7 days postischemic insult; C: brain tissue of animals treated with thioxanthenylcubane 7 days post ischemic insult. The box area designates the CA1region of the hippocampus.

FIGS. 3 a-3 d illustrate the neuroprotective effects of a thioxanthenylcubane (Compound 6) of the invention in the rat focal ischemia model.FIG. 3 a illustrates the effects of ischemic insult in the (i)hippocampus (ii) CA1 region (iii) retrosplenial cortex and (iv) piriformcortex of untreated animals (starch only); b: illustrates the effects ofischemic insult in the (i) hippocampus (ii) CA1 region (iii)retrosplenial cortex and (iv) piriform cortex of animals treated withone of the compounds of the invention 3 hours post ischemic insult(starch+test compound); c: illustrates the effects of focal ischemicinsult on neuronal cell number in the ipsilateral and contralateralsides of the CA1 region of animals treated with Compound 6 (i=0.1,ii=1.0, iii=10 mg/kg) 3 hours post ischemic insult; d: illustrates theeffects of focal ischemic insult on neuronal cell number in theipsilateral and contralateral sides of the CA1 region of animals treatedwith compound 6 (i=0.1, ii=1.0, iii=10 mg/kg) 0.5 hours pre, 0.5 and 3hours post ischemic insult.

FIG. 4 illustrates the anxiolytic effects of a thioxanthenyl cubane(compound 6) in the fear potentiated startle model (a=vehicle;b=diazepam; c−f=one of the thioxanthenyl cubane compounds at 1, 3, 10,15 mg/kg).

FIG. 5 illustrates the anxiolytic properties of a thioxanthenyl cubane(compound 6) in the fear induced freezing model. A: context alone; B:context plus tone.

FIG. 6 illustrates the anxiolytic properties of a thioxanthenyl cubane(compound 6) in social interaction studies. A: number of bites; B:number of pins (a−c=one of the thioxanthenyl cubane compounds (compound6) at 1, 3, 10 mg/kg; d=diazepam (2 mg/kg) and e=vehicle alone).

FIG. 7 illustrates the anxiolytic properties of a thioxanthenyl cubane(compound 6) in the elevated maze model, wherein time in open arm of themaze is measured (a−c=one of the thioxanthenyl cubane compounds(compound 6) at 1, 3, 10 mg/kg; d=diazepam (2 mg/kg) and e=vehiclealone).

FIG. 8 illustrates the anxiolytic properties of an orally administeredthioxanthenyl cubane (compound 6) in the fear potentiated startle model(a=control fear potentiated startle response; b=fear potentiated startleresponse in rats treated with 12 mg/kg of a thioxanthenyl cubanecompound).

FIG. 9 illustrates a dose response curve for an orally administeredthioxanthenyl cubane (compound 6) and comparison with diazepam in thefear potentiated startle model (a=vehicle alone; b=diazepam; c−f=one ofthe thioxanthenyl cubane compounds at 3, 7, 15, 30 mg/kg).

FIG. 10 illustrates the onset and duration of activity a thioxanthenylcubane (compound 6) in the fear potentiated startle model.

FIG. 11 illustrates the side effect profile of a thioxanthenyl cubane(compound 6) using the functional observational battery test, whereinthe greater the score, the greater the impairment (a=saline; b−e=one ofthe thioxanthenyl cubane compounds at 10, 20, 40 mg/kg; f−h=diazepam at2, 5, 8 mg/kg).

FIG. 12 illustrates the side effect profile of a thioxanthenyl cubane(compound 6) using the asymmetric grid test to measure impairment ofmotor function. A: forelimb errors; B: hindlimb errors (a−d=one of thethioxanthenyl cubane compounds at 0.3, 1.0, 3.0, 10.0 mg/kg; e=diazepamat 4 mg/kg; f=vehicle alone).

DETAILED DESCRIPTION OF THE INVENTION

The terms and abbreviations used in the instant examples have theirnormal meanings unless otherwise designated. For example “° C” refers todegrees Celsius; “N” refers to normal or normality; “mmol” refers tomillimole or millimoles; “g” refers to gram or grams; “mL” meansmilliliter or milliliters; “M” refers to molar or molarity; “MS” refersto mass spectrometry; “IR” refers to infrared spectroscopy; and “NMR”refers to nuclear magnetic resonance spectroscopy.

As would be understood by the skilled artisan throughout the synthesisof the compounds of the present invention, it may be necessary to employan amino-protecting group or a carboxy-protecting group in order toreversibly preserve a reactively susceptible amino or carboxyfunctionality while reacting other functional groups on the compound.

Examples of such amino-protecting groups include formyl, trityl,phthalimido, trichloroacetyl, chloroacetyl, bromoacetyl, iodoacetyl, andurethane-type blocking groups such as benzyloxycarbonyl,4-phenylbenzyloxycarbonyl, 2-methylbenzyloxycarbonyl,4-methoxybenzyloxycarbonyl, 4-fluorobenzyloxycarbonyl,4-chlorobenzyloxycarbonyl, 3-chlorobenzyloxycarbonyl,2-chlorobenzyloxycarbonyl, 2,4-dichlorobenzyloxycarbonyl,4-bromobenzyloxycarbonyl, 3-bromobenzyloxycarbonyl,4-nitrobenzyloxycarbonyl, 4-cyanobenzyloxycarbonyl, t-butoxycarbonyl,2-(4-xenyl)-isopropoxycarbonyl, 1,1-diphenyleth-1-yloxycarbonyl,1,1-diphenylprop-1-yloxycarbonyl, 2-phenylprop-2-yloxycarbonyl,2-(p-toluyl)-prop-2-yloxycarbonyl, cyclopentanyloxy-carbonyl,1-methylcyclopentanyloxycarbonyl, cyclohexanyloxycarbonyl,1-methylcyclohexanyloxycarbonyl, 2-methylcyclohexanyloxycarbonyl,2-(4-toluylsulfono)-ethoxycarbonyl, 2-(methylsulfono)ethoxycarbonyl,2-(triphenylphosphino)-ethoxycarbonyl, fluorenylmethoxycarbonyl(“FMOC”), 2-(trimethylsilyl)ethoxycarbonyl, allyloxycarbonyl,1-(trimethylsilylmethyl)prop-1-enyloxycarbonyl,5-benzisoxalylmethoxycarbonyl, 4-acetoxybenzyloxycarbonyl,2,2,2-trichloroethoxycarbonyl, 2-ethynyl-2-propoxycarbonyl,cyclopropylmethoxycarbonyl, 4-(decycloxy)benzyloxycarbonyl,isobornyloxycarbonyl, 1-piperidyloxycarbonlyl and the like;benzoylmethylsulfono group, 2-nitrophenylsulfenyl, diphenylphosphineoxide and like amino-protecting groups. The species of amino-protectinggroup employed is not critical so long as the derivatized amino group isstable to the condition of subsequent reaction(s) on other positions ofthe intermediate molecule and can be selectively removed at theappropriate point without disrupting the remainder of the moleculeincluding any other amino-protecting group(s). Preferredamino-protecting groups are t-butoxycarbonyl (t-Boc), allyloxycarbonyland benzyloxycarbonyl (CbZ). Further examples of these groups are foundin E. Haslam in Protective Groups in Organic Synthesis; McOmie, J. G.W., Ed. 1973, at Chapter 2; and Greene, T. W. and Wuts, P. G. M.,Protective Groups in Organic Synthesis, Second edition;Wiley-Interscience: 1991; Chapter 7.

Examples of such carboxyl-protecting groups include methyl,p-nitrobenzyl, p-methylbenzyl, p-methoxybenzyl, 3,4-dimethoxybenzyl,2,4-dimethoxybenzyl, 2,4,6-trimethoxybenzyl, 2,4,6-trimethylbenzyl,pentamethylbenzyl, 3,4-methylenedioxybenzyl, benzhydryl,4,4′-dimethoxybenzhydryl, 2,2′,4,4′-tetramethoxybenzhydryl, t-butyl,t-amyl, trittyl, 4-methoxytrityl, 4,4′-dimethoxytrityl,4,4′,4″-trimethoxytrityl, 2-phenylprop-2-yl, trimethylsilyl,t-butyldimethylsilyl, phenacyl, 2,2,2-trichloroethyl,β-(di(n-butyl)methylsilyl)ethyl, p-toluenesulfonoethyl,4-nitrobenzylsulfonoethyl, allyl, cinnamyl,I-(trimethylsilylmethyl)prop-1-en-3-yl and like moieties. Preferredcarboxyl-protecting groups are allyl, benzyl and t-butyl. Furtherexamples of these groups are found in E. Haslam, supra, at Chapter 5;and T. W. Greene and P. G. M. Wuts, supra, at Chapter 5.

Definitions

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention pertains.

The terms are defined as follows:

The term “halogen” refers to fluorine, bromine, chlorine, and iodineatoms.

The term “hydroxyl” refers to the group —OH.

The term “thiol” or “mercapto” refers to the group —SH.

The term “lower alkyl” refers to a straight chain or branched, orcyclic, alkyl group of one to ten carbon atoms. This term is furtherexemplified by such groups as methyl, ethyl, n-propyl, i-propyl,n-butyl, t-butyl, 1-butyl (or 2-methylpropyl), cyclopropylmethyl,i-amyl, n-amyl, hexyl and the like.

The term “substituted lower alkyl” refers to lower alkyl as justdescribed including one or more groups such as hydroxyl, thiol,alkylthiol, halogen, alkoxy, amino, amido, carboxyl, cycloalkyl,substituted cycloalkyl, heterocycle, cycloheteroalkyl, substitutedcycloheteroalkyl, acyl, carboxyl, aryl, substituted aryl, aryloxy,hetaryl, substituted hetaryl, aralkyl, heteroaralkyl, alkyl alkenyl,alkyl alkynyl, alkyl cycloalkyl, alkyl cycloheteroalkyl, cyano. Thesegroups may be attached to any carbon atom of the lower alkyl moiety.

The term “lower alkenyl” refers to a straight chain or branchedhydrocarbon of two to ten carbon atoms having at least one carbon tocarbon double bond.

The term “substituted lower alkenyl” refers to lower alkenyl as justdescribed including one or more groups such as hydroxyl, thiol,alkylthiol, halogen, alkoxy, amino, amido, carboxyl, cycloalkyl,substituted cycloalkyl, heterocycle, cycloheteroalkyl, substitutedcycloheteroalkyl, acyl, carboxyl, aryl, substituted aryl, aryloxy,hetaryl, substituted hetaryl, aralkyl, heteroaralkyl, alkyl, alkenyl,alkynyl, alkyl alkenyl, alkyl alkynyl, alkyl cycloalkyl, alkylcycloheteroalkyl, cyano. These groups may be attached to any carbon atomto produce a stable compound.

The term “lower alkynyl” refers to a straight chain or branchedhydrocarbon of two to ten carbon atoms having at least one carbon tocarbon triple bond.

The term “substituted lower alkynyl” refers to lower alkynyl as justdescribed including one or more groups such as hydroxyl, thiol,alkylthiol, halogen, alkoxy, amino, amido, carboxyl, cycloalkyl,substituted cycloalkyl, heterocycle, cycloheteroalkyl, substitutedcycloheteroalkyl, acyl, carboxyl, aryl, substituted aryl, aryloxy,hetaryl, substituted hetaryl, aralkyl, heteroaralkyl, alkyl, alkenyl,alkynyl, alkyl alkenyl, alkyl alkynyl, alkyl cycloalkyl, alkylcycloheteroalkyl, cyano. These groups may be attached to any carbon atomto produce a stable compound.

The term “alkoxy” refers to the group —OR, where R is lower alkyl,substituted lower alkyl, acyl, aryl, substituted aryl, aralkyl,substituted aralkyl, heteroalkyl, heteroarylalkyl, cycloalkyl,substituted cycloalkyl, cycloheteroalkyl, or substitutedcycloheteroalkyl as defined below.

The term “alkylthio” denotes the group —SR, —S(O)_(n=1-2)—R, where R islower alkyl, substituted lower alkyl, aryl, substituted aryl aralkyl orsubstituted aralkyl as defined below.

The term “acyl” refers to groups —C(O)R, where R is hydrogen, loweralkyl, substituted lower alkyl, aryl, substituted aryl.

The term “aryloxy” refers to groups —OAr, where Ar is an aryl,substituted aryl, heteroaryl, or substituted heteroaryl group as definedbelow.

The term “amino” refers to the group —NRR′, where R, R′ and R″ mayindependently be hydrogen, lower alkyl, substituted lower alkyl, aryl,substituted aryl, hetaryl, cycloalkyl, or substituted hetaryl as definedbelow or acyl.

The term “1° amino” refers to the group NRR′, where R and R′ are bothhydrogen.

The term “2° amino” refers to the group NRR′, where one of R and R′ isH.

The term “3° amino” refers to the group NRR′, where both R and R′ areother than H.

The term “quaternary ammonium salt” refers to the group —N⁺RR′R″, whereR, R′ and R″ may independently be hydrogen, lower alkyl, substitutedlower alkyl, aryl, substituted aryl, hetaryl, cycloalkyl, or substitutedhetaryl as defined below or acyl.

The term “amido” refers to the group —C(O)NRR′, where R and R′ mayindependently be hydrogen, lower alkyl, substituted lower alkyl, aryl,substituted aryl, hetaryl, substituted hetaryl as defined below.

The term “carboxyl” refers to the group —C(O)OR, where R mayindependently be hydrogen, lower alkyl, substituted lower alkyl, aryl,substituted aryl, hetaryl, substituted hetaryl and the like as defined.

The terms “aryl” or “Ar” refer to an aromatic carbocyclic group havingat least one aromatic ring (e.g., phenyl or biphenyl) or multiplecondensed rings in which at least one ring is aromatic, (e.g.,1,2,3,4-tetrahydronaphthyl, naphthyl, anthryl, or phenanthryl,9-fluorenyl etc.).

The term “substituted aryl” refers to aryl optionally substituted withone or more functional groups, e.g., halogen, hydroxyl, thiol, loweralkyl, substituted lower alkyl, trifluoromethyl, lower alkenyl,substituted lower alkenyl, lower alkynyl, substituted lower alkynyl,alkylalkenyl, alkyl alkynyl, alkoxy, alkylthio, acyl, aryloxy, amino,amido, carboxyl, aryl, substituted aryl, heterocycle, substitutedheterocycle, heteroaryl, substituted heteroaryl, heteroalkyl,substituted heteroalkyl, cycloalkyl, substituted cycloalkyl,alkylcycloalkyl, alkylcycloheteroalkyl, nitro, sulfamido or cyano.

The term “heterocycle” refers to a saturated, unsaturated, or aromaticcarbocyclic group having a single ring (e.g., morpholino, pyridyl orfuryl) or multiple condensed rings (e.g., naphthpyridyl, quinoxalyl,quinolinyl, indolizinyl, indanyl or benzo[b]thienyl) and having at leastone hetero atom, such as N, O or S, within the ring.

The term “substituted heterocycle” refers to heterocycle optionallysubstituted with, halogen, hydroxyl, thiol, lower alkyl, substitutedlower alkyl, trifluoromethyl, lower alkenyl, substituted lower alkenyl,lower alkynyl, substituted lower alkynyl, alkylalkenyl, alkyl alkynyl,alkoxy, alkylthio, acyl, aryloxy, amino, amido, carboxyl, aryl,substituted aryl, heterocycle, substituted heterocycle, heteroaryl,substituted heteroaryl, heteroalkyl, substituted heteroalkyl,cycloalkyl, substituted cycloalkyl, alkylcycloalkyl,alkylcycloheteroalkyl, nitro, sulfamido or cyano and the like.

The terms “heteroaryl” or “hetaryl” refer to a heterocycle in which atleast one heterocyclic ring is aromatic.

The term “substituted heteroaryl” refers to a heteroaryl as definedabove optionally substituted with one or more functional groups, e.g.,halogen, hydroxyl, thiol, lower alkyl, substituted lower alkyl,trifluoromethyl, lower alkenyl, substituted lower alkenyl, loweralkynyl, substituted lower alkynyl, alkylalkenyl, alkyl alkynyl, alkoxy,alkylthio, acyl, aryloxy, amino, amido, carboxyl, aryl, substitutedaryl, heterocycle, substituted heterocycle, heteroaryl, substitutedheteroaryl, heteroalkyl, substituted heteroalkyl, cycloalkyl,substituted cycloalkyl, alkylcycloalkyl, alkylcycloheteroalkyl, nitro,sulfamido or cyano and the like.

The term “aralkyl” refers to the group —R—Ar where Ar is an aryl groupand R is lower alkyl or substituted lower alkyl group. Aryl groups canoptionally be unsubstituted or substituted with, e.g., halogen, loweralkyl, alkoxy, alkyl thio, trifluoromethyl, amino, amido, carboxyl,hydroxyl, aryl, aryloxy, heterocycle, hetaryl, substituted hetaryl,nitro, cyano, alkylthio, thiol, sulfamido and the like.

The term “heteroalkyl” refers to the group —R-Het where Het is aheterocycle group and R is a lower alkyl group. Heteroalkyl groups canoptionally be unsubstituted or substituted with e.g., halogen, loweralkyl, lower alkoxy, lower alkylthio, trifluoromethyl, amino, amido,carboxyl, hydroxyl, aryl, aryloxy, heterocycle, hetaryl, substitutedhetaryl, nitro, cyano, alkylthio, thiol, sulfamido and the like.

The term “heteroarylalkyl” refers to the group —R-HetAr where HetAr isan heteroaryl group and R lower alkyl or substituted loweralkyl.Heteroarylalkyl groups can optionally be unsubstituted or substitutedwith, e.g., halogen, lower alkyl, substituted lower alkyl, alkoxy,alkylthio, aryl, aryloxy, heterocycle, hetaryl, substituted hetaryl,nitro, cyano, alkylthio, thiol, sulfamido and the like.

The term “cycloalkyl” refers to a cyclic or polycyclic alkyl groupcontaining 3 to 15 carbon. For polycyclic groups, these may be multiplecondensed rings in which one of the distal rings may be aromatic (e.g.tetrahydronaphthalene, etc.).

The term “substituted cycloalkyl” refers to a cycloalkyl groupcomprising one or more substituents with, e.g halogen, hydroxyl, thiol,lower alkyl, substituted lower alkyl, trifluoromethyl, lower alkenyl,substituted lower alkenyl, lower alkynyl, substituted lower alkynyl,alkylalkenyl, alkyl alkynyl, alkoxy, alkylthio, acyl, aryloxy, amino,amido, carboxyl, aryl, substituted aryl, heterocycle, heteroaryl,substituted heterocycle, heteroalkyl, cycloalkyl, substitutedcycloalkyl, alkylcycloalkyl, alkylcycloheteroalkyl, nitro, sulfamido orcyano and the like.

The term “cycloheteroalkyl” refers to a cycloalkyl group wherein one ormore of the ring carbon atoms is replaced with a heteroatom (e.g., N, O,S or P).

The term “substituted cycloheteroalkyl” refers to a cycloheteroalkylgroup as herein defined which contains one or more substituents, such ashalogen, lower alkyl, lower alkoxy, lower alkylthio, trifluoromethyl,amino, amido, carboxyl, hydroxyl, aryl, aryloxy, heterocycle, hetaryl,substituted hetaryl, nitro, cyano, alkylthio, thiol, sulfamido and thelike.

The term “alkyl cycloalkyl” refers to the group —R-cycloalkyl wherecycloalkyl is a cycloalkyl group and R is a lower alkyl or substitutedlower alkyl. Cycloalkyl groups can optionally be unsubstituted orsubstituted with e.g. halogen, lower alkyl, lower alkoxy, loweralkylthio, trifluoromethyl, amino, amido, carboxyl, hydroxyl, aryl,aryloxy, heterocycle, hetaryl, substituted hetaryl, nitro, cyano,alkylthio, thiol, sulfamido and the like.

The present invention provides a compound of the formula:

or a pharmaceutically acceptable salt or hydrate thereof, or apharmaceutically acceptable metabolically-labile ester or amide thereof,wherein:

-   R1 is an acidic group selected from the group consisting of    carboxyl, phosphono, phosphino, sulfono, sulfino, borono, tetrazol,    isoxazol, —CH₂-carboxyl, —CH₂-phosphono, —CH₂-phosphino,    —CH₂-sulfono, —CH₂-sulfino, —CH₂-borono, —CH₂-tetrazol,    —CH₂-isoxazol and higher analogues thereof;-   R2 is a basic group selected from the group consisting of 1° amino,    2° amino, 3° amino, quaternary ammonium salts, imidazol, guanidino,    boronoamino, allyl-urea, thiourea;-   R3 is of the formula;    -   wherein:        -   Y is absent or (CH₂)_(n) (where n=1-4), C═O, O, or NH;        -   X is O, NH, S, S═O, or SO₂;        -   R_(a), R_(b), R_(c), R_(d), R_(e), R_(f), R_(g) and R_(h)            are independently —H, hydroxyl, lower alkyl, substituted            lower alkyl, lower alkoxy, alkenyl, alkynyl, amino, halogen,            aryl, substituted aryl, nitrile, acyl, carboxy or amido;-   R4 is an acidic group selected from the group consisting of    carboxyl, phosphono, phosphino, sulfono, sulfino, borono, tetrazol,    isoxazol;-   and pharmaceutically acceptable salts thereof.

In another embodiment the substituents of the compound of formula (1)are as follows:

-   -   R1 is an acidic group selected from the group of carboxyl,        phosphono, phosphino, sulfono, sulfino, borono, tetrazol,        isoxazol, —CH₂-carboxyl, —CH₂-phosphono, —CH₂-phosphino,        —CH₂-sulfono, —CH₂-sulfino, —CH₂-borono, —CH₂-tetrazol, and        —CH₂-isoxazol;    -   R2 is a basic group selected from the group of 1° amino, 2°        amino, 3° amino, quaternary ammonium salts, imidazol, guanidino,        boronoamino, allyl,urea, thiourea, and NHR5, wherein R5 is —H or        an acyl group;    -   Y is (CH₂)_(n) and X is S, S═O or SO₂.

In another embodiment the substituents of the compound of formula (I)are as follows:

-   -   R1 is an acidic group selected from the group of carboxyl,        phosphono, phosphino, sulfono, sulfino, borono, tetrazol,        isoxazol, —CH₂-carboxyl, —CH₂-phosphono, —CH₂-phosphino,        —CH₂-sulfono, —CH₂-sulfino, —CH₂-borono, —CH₂-tetrazol, and        —CH₂-isoxazol;    -   R2 is a basic group selected from the group of 1° amino, 2°        amino, 30 amino, quaternary ammonium salts, imidazol, guanidino,        boronoamino, allylurea, thiourea, and NHR5, wherein R5 is —H or        an acyl group;    -   Y is (CH₂)_(n) and X is O or NH,.

In another embodiment in the compound of formula (I), when X═S andY═CH₂, then at least one of R_(a) through R_(h) is other than —H.

In another embodiment in the compound of formula (I), when X═O andY═CH₂, then at least one of R_(a) through R_(h) is other than —H.

In another embodiment in the compound of formula (I), when X═S and Y isabsent or (CH₂)_(n) then at least one of R_(a) through R_(h) is otherthan —H.

In another embodiment in the compound of formula (I), when X═O and Y isabsent or ═(CH₂)₂, then at least one of R_(a) through R_(h) is otherthan —H.

In another embodiment the substituents of the compound of formula (I)are as follows:

-   -   R1 is an acidic group selected from the group of carboxyl,        phosphono, phosphino, sulfono, sulfino, borono, tetrazol,        isoxazol, —CH₂-carboxyl, —CH₂-phosphono, —CH₂-phosphino,        —CH₂-sulfono, —CH₂-sulfino, —CH₂-borono, —CH₂-tetrazol, and        —CH₂-isoxazol;    -   R2 is a basic group selected from the group of 10 amino, 20        amino, 3° amino, quaternary ammonium salts, imidazol, guanidino,        boronoamino, allylurea, thiourea, and NHR5, wherein R5 is —H or        an acyl group;    -   Y is C═O and X is O, NH, S, S═O or SO₂.

In another embodiment the substituents of the compound of formula (I)are as follows:

-   -   R1 is an acidic group selected from the group of carboxyl,        phosphono, phosphino, sulfono, sulfino, borono, tetrazol,        isoxazol, —CH₂-carboxyl, —CH₂-phosphono, —CH₂-phosphino,        —CH₂-sulfono, —CH₂-sulfino, —CH₂-borono, —CH₂-tetrazol, and        —CH₂-isoxazol;    -   R2 is a basic group selected from the group of 1° amino, 2°        amino, 3° amino, quaternary ammonium salts, imidazol, guanidino,        boronoamino, allylurea, thiourea, and NHR5, wherein R5 is —H or        an acyl group;    -   Y is O or NH and X is O, NH, S, S═O or SO₂.

In another embodiment the substituents of the compound of formula (1)are as follows:

-   -   R1 is an acidic group selected from the group of carboxyl,        phosphono, phosphino, sulfono, sulfino, borono, tetrazol,        isoxazol, —CH₂-carboxyl, —CH₂-phosphono, —CH₂-phosphino,        —CH₂-sulfono, —CH₂-sulfino, —CH₂-borono, —CH₂-tetrazol, and        —CH₂-isoxazol;    -   R2 is a basic group selected from the group of 1° amino, 2°        amino, 3° amino, quaternary ammonium salts, imidazol, guanidino,        boronoamino, allylurea, thiourea, and NHR5, wherein R5 is —H or        an acyl group;    -   Y is (CH₂)_(n) and X is S.

In another embodiment, in the compound of formula (I), when X is S, thenY is C═O, O or NH.

In another embodiment, in the compound of formula (I), when X is O, thenY is C═O, O or NH.

In another embodiment the compound of formula (I) is:

wherein:

-   R1 is carboxy or —CH₂-carboxy;-   R2 is 1° amino, 2° amino, 3° amino;-   R3 is xanthenyl or thioxanthenyl or —CH₂-xanthenyl or    —CH₂-thioxanthenyl-   R4 is carboxy.

In another embodiment the compound of formula (I) is:

wherein:

-   R1 is COOH or —CH₂—COOH-   R2 is NH₂-   R3 is xanthenyl or thioxanthenyl or —CH₂-xanthenyl or    —CH₂-thioxanthenyl-   R4 is COOH

While all of the compounds of the present invention demonstrate activityat the metabotropic glutamate receptors (mGluRs), certain groups of saidcompounds are more preferred for such use.

The compounds of the present invention are agonists or antagonists atcertain metabotropic excitatory amino acid receptors (mGluRs). When acompound of the invention acts as an agonist, the interaction of thecompound with the excitatory amino acid receptor mimics the response ofthe interaction of this receptor with its natural ligand (i.e.L-Glutamic acid). When a compound of the invention acts as anantagonist, the interaction of the compound with the excitatory aminoacid receptor blocks the response of the interaction of this receptorwith its natural ligand (i.e. L-Glutamic acid). The compounds of thepresent invention may also act as antagonists of particular mGluRsgroups while also acting as agonists of other mGluRs groups.

As noted above, this invention includes the pharmaceutically acceptablesalts of the compounds defined by Formula I. A compound of thisinvention can possess a sufficiently acidic, a sufficiently basic, orboth functional groups, and accordingly react with any of a number oforganic and inorganic bases, and inorganic and organic acids, to form apharmaceutically acceptable salt.

The term “pharmaceutically acceptable salt” as used herein, refers tosalts of the compounds of the above formula which are substantiallynon-toxic to living organisms. Typical pharmaceutically acceptable saltsinclude those salts prepared by reaction of the compounds of the presentinvention with a pharmaceutically acceptable mineral or organic acid oran organic or inorganic base. Such salts are known as acid addition andbase addition salts.

Acids commonly employed to form acid addition salts are inorganic acidssuch as hydrochloric acid, hydrobromic acid, hydriodic acid, sulfuricacid, phosphoric acid, and the like, and organic acids such asp-toluenesulfonic acid, methanesulfonic acid, oxalic acid,p-bromophenylsulfonic acid, carbonic acid, succinic acid, citric acid,benzoic acid, acetic acid, and the like. Examples of suchpharmaceutically acceptable salts are the sulfate, pyrosulfate,bisulfate, sulfite, bisulfite, phosphate, monohydrogenphosphate,dihydrogenphosphate, metaphosphate, pyrophosphate, bromide, iodide,acetate, propionate, decanoate, caprylate, acrylate, formate,hydrochloride, dihydrochloride, isobutyrate, caproate, heptanoate,propiolate, oxalate, malonate, succinate, suberate, sebacate, fumarate,maleate, butyne-1,4-dioate, hexyne-1,6-dioate, benzoate, chlorobenzoate,methylbenzoate, hydroxybenzoate, methoxybenzoate, phthalate,xylenesulfonate, phenylacetate, phenylpropionate, phenylbutyrate,citrate, lactate, gamma-hydroxybutyrate, glycolate, tartrate,methanesulfonate, propanesulfonate, naphthalene-1-sulfonate,napththalene-2-sulfonate, mandelate and the like. Preferredpharmaceutically acceptable acid addition salts are those formed withmineral acids such as hydrochloric acid and hydrobromic acid, and thoseformed with organic acids such as maleic acid and methanesulfonic acid.

Salts of amine groups may also comprise quarternary ammonium salts inwhich the amino nitrogen carries a suitable organic group such as analkyl, alkenyl, alkynyl, or aralkyl moiety.

Base addition salts include those derived from inorganic bases, such asammonium or alkali or alkaline earth metal hydroxides, carbonates,bicarbonates, and the like. Such bases useful in preparing the salts ofthis invention thus include sodium hydroxide, potassium hydroxide,ammonium hydroxide, potassium carbonate, sodium carbonate, sodiumbicarbonate, potassium bicarbonate, calcium hydroxide, calciumcarbonate, and the like. The potassium and sodium salt forms areparticularly preferred.

It should be recognized that the particular counterion forming a part ofany salt of this invention is usually not of a critical nature, so longas the salt as a whole is pharmacologically acceptable and as long asthe counterion does not contribute undesired qualities to the salt as awhole. This invention further encompasses the pharmaceuticallyacceptable solvates of the compounds of Formula I. Many of the Formula Icompounds can combine with solvents such as water, methanol, ethanol andacetonitrile to form pharmaceutically acceptable solvates such as thecorresponding hydrate, methanolate, ethanolate and acetonitrilate.

The compounds of the present invention have multiple asymmetric (chiral)centers. As a consequence of these chiral centers, the compounds of thepresent invention occur as racemates, mixtures of enantiomers and asindividual enantiomers, as well as diastereomers and mixtures ofdiastereomers. All asymmetric forms, individual isomers and combinationsthereof, are within the scope of the present invention.

The prefixes “R” and “S” are used herein as commonly used in organicchemistry to denote the absolute configuration of a chiral center,according to the Cahn-Ingold-Prelog system. The stereochemicaldescriptor R (rectus) refers to that configuration of a chiral centerwith a clockwise relationship of groups tracing the path from highest tosecond-lowest priorities when viewed from the side opposite to that ofthe lowest priority group. The stereochemical descriptor S (sinister)refers to that configuration of a chiral center with a counterclockwiserelationship of groups tracing the path from highest to second-lowestpriority when viewed from the side opposite to the lowest prioritygroup. The priority of groups is decided using sequence rules asdescribed by Cahn et al., Angew. Chem., 78, 413-447, 1966 and Prelog, V.and Helmchen, G.; Angew. Chem. Int. Ed. Eng., 21, 567-583, 1982).

In addition to the R,S system used to designate the absoluteconfiguration of a chiral center, the older D-L system is also used inthis document to denote relative configuration, especially withreference to amino acids and amino acid derivatives. In this system aFischer projection of the compound is oriented so that carbon-1 of theparent chain is at the top. The prefix “D” is used to represent therelative configuration of the isomer in which the functional(determining) group is on the right side of the carbon atom at thechiral center and “L”, that of the isomer in which it is on the left.

As would be expected, the stereochemistry of the Formula I compounds iscritical to their potency as agonists or antagonists. The relativestereochemistry is established early during synthesis, which avoidssubsequent stereoisomer separation problems later in the process.Further manipulation of the molecules then employs stereospecificprocedures so as to maintain the preferred chirality. The preferredmethods of this invention are the methods employing those preferredcompounds.

Non-toxic metabolically-labile esters and amides of compounds of FormulaI are ester or amide derivatives of compounds of Formula I that arehydrolyzed in vivo to afford said compounds of Formula I and apharmaceutically acceptable alcohol or amine. Examples ofmetabolically-labile esters include esters formed with (1-6C) alkanolsin which the alkanol moiety may be optionally substituted by a (1-8C)alkoxy group, for example methanol, ethanol, propanol andmethoxyethanol. Examples of metabolically-labile amides include amidesformed with amines such as methylamine.

According to another aspect, the present invention provides a processfor the preparation of a compound of Formula I, or a pharmaceuticallyacceptable metabolically-labile ester or amide thereof, or apharmaceutically acceptable salt thereof, which comprises:

-   (a) hydrolyzing a compound of formula (IIa):    wherein: R′1 is an acidic group selected from the group consisting    of carboxyl, phosphono, phosphino, sulfono, sulfino, borono,    tetrazol, isoxazol, —CH₂-carboxyl, —CH₂-phosphono, —CH₂-phosphino,    —CH₂-sulfono, —CH₂-sulfino, —CH₂-borono, —CH₂-tetrazol,    —CH₂-isoxazol and higher analogues thereof, or a protected form    thereof, RS represents a hydrogen atom or an acyl group and R3 has    the meaning defined above. Preferred values for R5 are hydrogen and    (2-6C) alkanoyl groups, such as acetyl, or-   (b) by deprotecting and hydrolyzing a compound of formula (II b)    wherein, R′1 and R3 are as defined above, or-   (c) hydrolyzing a compound of formula:    wherein: R′1 and R3 are as defined above R6 and R7 each    independently represent a hydrogen atom, a (2-6C) alkanoyl group, a    (1-4C) alkyl group, a (3-4C) alkenyl group or a phenyl (1-4C) alkyl    group in which the phenyl is unsubstituted or substituted by    halogen, (1-4C) alkyl or (1-4C) alkoxy, or a salt thereof; or-   (d) deprotecting a compound of formula:    wherein; R′1 and R3 are as defined above, R8 represents a hydrogen    atom or a carboxyl protecting group, or a salt thereof, and R9    represents a hydrogen atom or a nitrogen protecting group;-   whereafter, if necessary and/or desired:-   (i) resolving the compound of Formula I;-   (ii) converting the compound of Formula I into a non-toxic    metabolically-labile ester or amide thereof; and/or;-   (iii) converting the compound of Formula I or a non-toxic    metabolically-labile ester or amide thereof into a pharmaceutically    acceptable salt thereof.

The protection of carboxylic acid and amine groups is generallydescribed in McOmie, Protecting Groups in Organic Chemistry, PlenumPress, NY, 1973, and Greene and Wuts, Protecting Groups in OrganicSynthesis, 2nd. Ed., John Wiley & Sons, NY, 1991. Examples of carboxylprotecting groups include alkyl groups such as methyl, ethyl, t-butyland t-amyl; aralkyl groups such as benzyl, 4-nitrobenzyl,4-methoxybenzyl, 3,4-dimethoxybenzyl, 2,4-dimethoxybenzyl,2,4,6-trimethoxybenzyl, 2,4,6-trimethylbenzyl, benzhydryl and trityl;silyl groups such as trimethylsilyl and 1-butyldimethylsilyl; and allylgroups such as allyl and 1-(trimethylsilylmethyl)prop-1-en-3-yl.

Examples of amine-protecting groups include acyl groups, such as groupsof formula R9—CO in which R9 represents (1-6C) alkyl, (3-10C)cycloalkyl, phenyl(1-6C) alkyl, phenyl(1-6C) alkoxy, or a (3-10C)cycloalkoxy, wherein a phenyl group may optionally be substituted by oneor two substituents independently selected from amino, hydroxy, nitro,halogeno, (1-6C) alkyl, (1-6C) alkoxy, carboxyl, (1-6C) alkoxycarbonyl,carbamoyl, (1-6C) alkanoylamino, (1-6C) alkylsulphonylamino,phenylsulphonylamino, toluenesulphonylamino, and (1-6C) fluoroalkyl.

The compounds of Formula II are conveniently hydrolyzed in the presenceof an acid, such as hydrochloric acid or sulfuric acid, or a base, suchas an alkali metal hydroxide, for example sodium hydroxide. Thehydrolysis is conveniently performed in an aqueous solvent such as waterand at a temperature in the range of 50 to 200° C.

The compounds of Formula III are conveniently hydrolyzed in the presenceof a base, for example an alkali metal hydroxide such as lithium, sodiumor potassium hydroxide, or an alkaline earth metal hydroxide such asbarium hydroxide. Suitable reaction media include water. The temperatureis conveniently in the range of from 50 to 150° C.

The compounds of Formula IV may be deprotected by a conventional method.Thus, an alkyl carboxyl protecting group may be removed by hydrolysis.The hydrolysis may conveniently be performed by heating the compound ofFormula IV in the presence of either a base, for example an alkali metalhydroxide such as lithium, sodium or potassium hydroxide, or an alkalinemetal hydroxide, such as barium hydroxide, or an acid such ashydrochloric acid. The hydrolysis is conveniently performed at atemperature in the range from 10 to 300° C. An aralkyl carboxylprotecting group may conveniently be removed by hydrogenolysis. Thehydrogenolysis may conveniently be effected by reacting the compound ofFormula IV with hydrogen in the presence of a Group VIII metal catalyst,for example a palladium catalyst such as palladium on charcoal. Suitablesolvents for the reaction include alcohols such as ethanol. The reactionis conveniently performed at a temperature in the range from 0 to 100°C. An acyl, amine protecting group is also conveniently removed byhydrolysis, for example as described for the removal of an alkylcarboxyl protecting group.

The compounds of Formula II may be prepared by reacting a compound offormula:

with an alkali metal cyanide, such as lithium, sodium or potassiumcyanide, and an ammonium halide, such as ammonium chloride, convenientlyin the presence of ultrasound. Thus, the ammonium halide is mixed withchromatography grade alumina in the presence of a suitable diluent suchas acetonitrile. The mixture is then irradiated with ultrasound,whereafter the compound of Formula V is added, and the mixture is againirradiated. The alkali metal cyanide is then added, followed by furtherirradiation with ultrasound.

Individual isomers of compounds of Formula I may be made by reacting acompound of the Formula V with the stereoisomers of the chiral agent(S)— and (R)-phenylglycinol and a reactive cyanide such astrimethylsilyl cyanide.

The compounds of Formula III may be prepared by reacting a compound ofFormula V with an alkali metal cyanide, such as lithium, sodium orpotassium cyanide, and ammonium carbonate or ammonium carbamate.Convenient solvents include water, dilute ammonium hydroxide, alcoholssuch as methanol, aqueous methanol and aqueous ethanol. Conveniently thereaction is performed at a temperature in the range of from 10 to 150°C. If desired, the compounds of Formula III may then be alkylated, forexample using an appropriate compound of formula R6 Cl and/or R7 Cl.

The compounds of Formula V can be prepared by reacting a compound offormula:

with a chlorinating agent such as thionyl chloride or phosphorous (V)chloride, followed by reaction with organo copper or organo metal orGrignard reagent derived from R3X or by reaction with ethyl hydrogenmalonate in the presence of organolithium, wherein R3 has the meaningdefined above and X is halogen.

The compounds of Formula V can also be prepared by oxidizing a compoundof formula

under Swern conditions.

The compounds of Formula VI can be prepared from compounds of formula:

by reduction.

When R′1 is CO₂Me, this compound can be bought commercially. When R′1 isanother substituent, the compound of Formula VIII can be made usingstandard procedures.

Many of the intermediates described herein, for example the compounds ofFormula II, m and IV are to be novel, and are provided as furtheraspects of the invention.

The compounds of the present invention are metabotropic excitatory aminoacid receptor modulators which when administered in prophylactically ortherapeutically effective doses to a mammal in need of such therapyexhibit anxiolytic or neuroprotective properties.

The compounds of the present invention are agonists or antagonists atcertain metabotropic excitatory amino acid receptors (mGluRs).Therefore, another aspect of the present invention is a method ofaffecting mGluRs in mammals, which comprises administering to a mammalrequiring modulated excitatory amino acid neurotransmission apharmacologically-effective amount of a compound of the invention. Theterm “pharmacologically-effective amount” is used to represent an amountof the compound of the invention that is capable of affecting themGluRs. By affecting, a compound of the invention is acting as anagonist or antagonist. When a compound of the invention acts as anagonist, the interaction of the compound with the excitatory amino acidreceptor mimics the response of the interaction of this receptor withits natural ligand (i.e. L-Glutamic acid). When a compound of theinvention acts as an antagonist, the interaction of the compound withthe excitatory amino acid receptor blocks the response of theinteraction of this receptor with its natural ligand (i.e. L-Glutamicacid).

The compounds of the present invention may also act as antagonists ofparticular mGluRs groups while also acting as agonists of other mGluRsgroups. The particular dose of compound administered according to thisinvention will, of course, be determined by the particular circumstancessurrounding the case, including the compound administered, the route ofadministration, the particular condition being treated, and similarconsiderations. The compounds can be administered by a variety of routesincluding oral, rectal, transdermal, subcutaneous, intravenous,intramuscular, or intranasal routes. Alternatively, the compound may beadministered by continuous infusion. A typical daily dose will containfrom about 0.001 mg/kg to about 100 mg/kg of the active compound of thisinvention. Preferably, daily doses will be about 0.05 mg/kg to about 50mg/kg, more preferably from about 0.1 mg/kg to about 20 mg/kg.

A variety of physiological functions have been shown to be subject toinfluence by excessive or inappropriate stimulation of excitatory aminoacid transmission. The compounds of the present invention (through theirinteractions at the mGluRs) have the ability to treat a variety ofneurological disorders in mammals associated with this condition,including acute neurological disorders such as cerebral deficitssubsequent to cardiac bypass surgery and grafting, cerebral ischemia(e.g. stroke and cardiac arrest), spinal cord trauma, head trauma,perinatal hypoxia, ischemia related neuropathies from surgicalprocedures or micro-emboli and hypoglycemic neuronal damage. Thecompounds of the present invention have the ability to treat a varietyof chronic neurological disorders, such as Alzheimer's disease,Huntington's Chorea, amyotrophic lateral sclerosis, AIDS-induceddementia, ocular damage, glaucoma, macular degeneration and retinopathy,cognitive disorders, and idiopathic and drug-induced Parkinson'sdisease. The present invention also provides methods for treating thesedisorders which comprises administering to a patient in need thereof aneffective amount of a compound of the present invention.

The compounds of the present invention (through their interactions atthe mGluRs) are also able to treat a variety of other neurologicaldisorders in mammals that are associated with glutamate dysfunction,including muscular spasms, convulsions, migraine headaches, urinaryincontinence, psychosis, drug tolerance, withdrawal, and cessation (i.e.opiates, benzodiazepines, nicotine, cocaine, or ethanol), smokingcessation, anxiety and related disorders (e.g. panic attack), emesis,brain edema, chronic pain, sleep disorders, Tourette's syndrome,attention deficit disorder, and tardive dyskinesia. Therefore, thepresent invention also provides methods for treating these disorderswhich comprise administering to a patient in need thereof an effectiveamount of the compound of the invention.

The compounds of the present invention (through their interactions atthe mGluRs) are also able to treat a variety of psychiatric disorders,such as schizophrenia, anxiety and related disorders (e.g. panicattack), depression, bipolar disorders, psychosis, and obsessivecompulsive disorders. The present invention also provides methods fortreating these disorders which comprises administering to a patient inneed thereof an effective amount of a compound of the invention.

In addition to acting therapeutically, the compounds of the presentinvention act prophylactically as a neuroprotectant. The compounds ofthe present invention, through their interaction at the mGluRs, limitneuronal cell death following anoxic insult. Therefore the presentinvention provides both methods for prophylactically and therapeuticallypreventing neuronal cell death which comprises administering to apatient in need of such therapy a prophylactically or a therapeuticallyeffective amount of the compounds of the invention.

The pharmacological properties of the compounds of the invention can beillustrated by determining their effects in various functional in vitroassays. The compounds of the invention were studied in an in vitro assaythat measured the inhibition of PI hydrolysis or the formation of cyclicAMP in Chinese hamster ovary cell lines expressing mGluR_(1α), mGluR₂and mGluR_(4a) cloned metabotropic glutamate receptors.

The ability of a candidate compound to inhibit neuronal cell death canbe examined using an in vitro anoxia study. Briefly, cell counts can beconducted at various time points following exposure of a neuronal cellculture to anoxic conditions to determine if a candidate compoundexhibits neuroprotective activity. A candidate compound can beadministered to the neuronal cell culture at various time points priorto exposure to the anoxic condition to examine the prophylactic activityof the compound or during or after exposure to the anoxic condition toexamine therapeutic activity of the compound. Suitable negative controlsinclude, for example, buffer in place of the candidate compound.

The neuroprotective effects of a candidate compound can also beevaluated in a number of in vivo animal models including, the rat globalischemia model. Briefly, two of the four cerebral arteries arepermanently occluded and surgical silk is loosely placed around theremaining two cerebral arteries. Temporary tightening of the surgicalsilk leads to 4 vessel occlusion and temporary global ischemia. Atvarious time points after ischemic insult the brain can be removed andexamined for ischemic injury.

Alternatively, the starch microsphere infusion focal ischemia model canbe used. Briefly, starch microspheres are injected unilaterally into oneof the carotid arteries. Blood flow is temporarily occluded on theinjected side for approximately 30 minutes. Reperfusion occurs after theinitial starch clot is resolved. At various time points after ischemicinsult the brain can be removed and examined for ischemic injury.

The candidate compounds can be administered at various time points priorto ischemic insult (in both the rat global ischemia model and focalischemia model) to examine the prophylactic activity of a candidatecompound or after ischemic insult to examine therapeutic activity of acandidate compound. Suitable negative controls include, for example,buffer in place of the candidate compound.

The anxiolytic properties of a candidate compound can be examined usinga variety of tests, including but not limited to, the fear potentiatedstartle test, fear induced freezing tests, social interaction studiesand the elevated plus maze test.

The fear potentiated startle model permits measurement of learned fearof a stimulus that has been paired with repeated foot shocks. The effectof a candidate compound on fear potentiated startle can be compared witha known standard such as diazepam and a negative control (such as bufferonly). The fear potentiated startle test can be conducted at varioustime points following administration of a candidate compound.

The anxiolytic properties of a candidate compound can also be examinedusing the fear induced freezing model. Briefly, this test relies on theinduction of a well known effect in rats when they are challenged. Therat is subjected to a mild shock associated with a sound which resultsin the animal becoming very still when expecting that shock. The effectof a candidate compound on fear induced freezing can be compared with aknown standard such as diazepam and a negative control (such as bufferonly). The fear induced freezing test can be conducted at various timepoints following administration of the candidate compound.

The effect of a candidate compound on social interaction can also beexamined in rodents. Briefly, social interaction can be measured asfollows: a strange intruder is introduced into the cage of anacclimatized treated rat and the number of times the rat either bites (#bites) or wrestles (# pins) the intruder is determined. The effect of acandidate compound on social interaction can be compared with a knownstandard such as diazepam and a negative control (such as buffer only).The social interaction test can be conducted at various time pointsfollowing administration of the candidate compound.

The anxiolytic properties of candidate compounds can be furtherevaluated using the elevated plus maze test. This test is dependent onthe predisposition of rodents to remain in the dark and offers thechoice between dark areas of the maze and the opportunity to explorelighted areas. The effect of a candidate compound on the elevated plusmaze test can be compared with a known standard such as diazepam and anegative control (such as buffer only). The elevated maze plus test canbe conducted at various time points following administration of thecandidate compound.

The compounds of the present invention have been evaluated in a ratmodel of focal ischemia which is similar to that seen in strokes inhumans. Briefly, starch microspheres are injected unilaterally into oneof the carotid arteries. Blood flow is temporarily occluded on theinjected side for approximately 30 minutes. Reperfusion occurs after theinitial starch clot is resolved. The test compound is administeredeither prophylactically before vessel occlusion or therapeutically postvessel occlusion.

According to another aspect, the present invention provides a method ofmodulating one or more metabotropic glutamate receptor functions in awarm-blooded mammal which comprises administering an effective amount ofa compound of the invention, or a non-toxic metabolically-labile esteror amide thereof, or a pharmaceutically acceptable salt thereof.

The compounds of the present invention are preferably formulated priorto administration. Therefore, another aspect of the present invention isa pharmaceutical formulation comprising a compound of the presentinvention and a pharmaceutically-acceptable carrier, diluent, orexcipient. The present pharmaceutical formulations are prepared by knownprocedures using well-known and readily available ingredients. In makingthe compositions of the present invention, the active ingredient willusually be mixed with a carrier, or diluted by a carrier, or enclosedwithin a carrier, and may be in the form of a capsule, sachet, paper, orother container. When the carrier serves as a diluent, it may be asolid, semi-solid, or liquid material that acts as a vehicle, excipient,or medium for the active ingredient. The compounds of the presentinvention are usually administered in the form of pharmaceuticalcompositions. These compounds can be administered by a variety of routesincluding oral, rectal, transdermal, subcutaneous, intravenous,intramuscular, and intranasal. These compounds are effective as bothinjectable and oral compositions. Such compositions are prepared in amanner well known in the pharmaceutical art and comprise at least oneactive compound.

The present invention also provides pharmaceutical compositionscontaining compounds as disclosed in the claims in combination with oneor more pharmaceutically acceptable, inert or physiologically active,diluent or adjuvant. The compounds of the invention can be freeze-driedand, if desired, combined with other pharmaceutically acceptableexcipients to prepare formulations for administration. Thesecompositions may be presented in any form appropriate for theadministration route envisaged. The parenteral and the intravenous routeare the preferential routes for administration.

Compounds of the present invention may be administered orally,topically, parenterally, by inhalation or spray or rectally in dosageunit formulations containing conventional non-toxic pharmaceuticallyacceptable carriers, adjuvants and vehicles. The term parenteral as usedherein includes subcutaneous injections, intravenous, intramuscular,intrasternal injection or infusion techniques. In addition, there isprovided a pharmaceutical formulation comprising a compound of theinvention and a pharmaceutically acceptable carrier. One or morecompounds of the invention may be present in association with one ormore non-toxic pharmaceutically acceptable carriers and/or diluentsand/or adjuvants and if desired other active ingredients. Thepharmaceutical compositions containing compounds of the invention may bein a form suitable for oral use, for example, as tablets, troches,lozenges, aqueous or oily suspensions, dispersible powders or granules,emulsions, hard or soft capsules, or syrups or elixirs.

Compositions intended for oral use may be prepared according to anyknown to the art for the manufacture of pharmaceutical compositions andsuch compositions may contain one or more agents selected from the groupconsisting of sweetening agents, flavouring agents, colouring agents andpreserving agents in order to provide pharmaceutically elegant andpalatable preparations. Tablets contain the active ingredient inadmixture with non-toxic pharmaceutically acceptable excipients that aresuitable for the manufacture of tablets. These excipients may be forexample, inert diluents, such as calcium carbonate, sodium carbonate,lactose, calcium phosphate or sodium phosphate: granulating anddisintegrating agents for example, corn starch, or alginic acid: bindingagents, for example starch, gelatin or acacia, and lubricating agents,for example magnesium stearate, stearic acid or talc. The tablets may beuncoated or they may be coated by known techniques to delaydisintegration and absorption in the gastrointestinal tract and therebyprovide a sustained action over a longer period. For example, a timedelay material such as glyceryl monostearate or glyceryl distearate maybe employed.

Formulations for oral use may also be presented as hard gelatin capsuleswherein the active ingredient is mixed with an inert solid diluent, forexample, calcium carbonate, calcium phosphate or kaolin, or as softgelatin capsules wherein the active ingredient is mixed with water or anoil medium, for example peanut oil, liquid paraffin or olive oil.

Aqueous suspensions contain active materials in admixture withexcipients suitable for the manufacture of aqueous suspensions. Suchexcipients are suspending agents, for example sodiumcarboxylmethylcellulose, methyl cellulose, hydropropylmethylcellulose,sodium alginate, polyvinylpyrrolidone, gum tragacanth and gum acacia:dispersing or wetting agents may be a naturally-occurring phosphatide,for example, lecithin, or condensation products of an alkylene oxidewith fatty acids, for example polyoxyethylene stearate, or condensationproducts of ethylene oxide with long chain aliphatic alcohols, forexample hepta-decaethyleneoxycetanol, or condensation products ofethylene oxide with partial esters derived from fatty acids and ahexitol such as polyoxyethylene sorbitol monooleate, or condensationproducts of ethylene oxide with partial esters derived from fatty acidsand hexitol anhydrides, for example polyethylene sorbitan monooleate.The aqueous suspensions may also contain one or more preservatives, forexample ethyl, or n-propyl- p-hydroxy benzoate, one or more colouringagents, one or more flavouring agents or one or more sweetening agents,such as sucrose or saccharin.

Oily suspensions may be formulated by suspending the active ingredientsin a vegetable oil, for example peanut oil, olive oil, sesame oil orcoconut oil, or in a mineral oil such as liquid paraffin. The oilysuspensions may contain a thickening agent, for example beeswax, hardparaffin or cetyl alcohol. Sweetening agents such as those set forthabove, and flavouring agents may be added to provide palatable oralpreparations. These compositions may be preserved by the addition of ananti-oxidant such as ascorbic acid.

Dispersible powders and granules suitable for preparation of an aqueoussuspension by the addition of water provide the active ingredient inadmixture with a dispersing or wetting agent, suspending agent and oneor more preservatives. Suitable dispersing or wetting agents andsuspending agents are exemplified by those already mentioned above.Additional excipients, for example sweetening, flavouring and colouringagents, may also be present.

Pharmaceutical compositions of the invention may also be in the form ofoil-in-water emulsions. The oil phase may be a vegetable oil, forexample olive oil or peanut oil, or a mineral oil, for example liquidparaffin or mixtures of these. Suitable emulsifying agents may benaturally-occurring gums, for example gum acacia or gum tragacanth,naturally-occurring phosphatides, for example soy bean, lecithin, andesters or partial esters derived from fatty acids and hexitol,anhydrides, for example sorbitan monooleate, and condensation productsof the said partial esters with ethylene oxide, for examplepolyoxyethylene sorbitan monooleate. The emulsions may also containsweetening and flavouring agents.

Syrups and elixirs may be formulated with sweetening agents, for exampleglycerol, propylene glycol, sorbitol or sucrose. Such formulations mayalso contain a demulcent, a preservative and flavouring and colouringagents. The pharmaceutical compositions may be in the form of a sterileinjectable aqueous or oleaginous suspension. This suspension may beformulated according to known art using those suitable dispersing orwetting agents and suspending agents that have been mentioned above. Thesterile injectable preparation may also be a sterile injectable solutionor a suspension in a non-toxic parentally acceptable diluent or solvent,for example as a solution in 1,3-butanediol. Among the acceptablevehicles and solvents that may be employed are water, Ringer's solutionand isotonic sodium chloride solution. In addition, sterile, fixed oilsare conventionally employed as a solvent or suspending medium. For thispurpose any bland fixed oil may be employed including synthetic mono- ordiglycerides. In addition, fatty acids such as oleic acid find use inthe preparation of injectables.

The compounds of the present invention may be administered, together orseparately, in the form of suppositories for rectal administration ofthe drug. These compositions can be prepared by mixing the drug with asuitable non-irritating excipient which is solid at ordinarytemperatures but liquid at the rectal temperature and will thereforemelt in the rectum to release the drug. Such materials are cocoa butterand polyethylene glycols.

Compounds of the present invention may be administered, together orseparately, parenterally in sterile medium. The drug, depending on thevehicle and concentration used, can either be suspended or dissolved inthe vehicle. Advantageously, adjuvants such as local anaesthetics,preservatives and buffering agents can be dissolved in the vehicle.

The dosage to be administered is not subject to defined limits, but itwill usually be an effective amount. It will usually be the equivalent,on a molar basis of the pharmacologically active free form produced froma dosage formulation upon the metabolic release of the active free drugto achieve its desired pharmacological and physiological effects. Thecompositions are preferably formulated in a unit dosage form, eachdosage containing from about 0.05 to about 100 mg, more usually about1.0 to about 30 mg, of the active ingredient. The term “unit dosageform” refers to physically discrete units suitable as unitary dosagesfor human subjects and other mammals, each unit containing apredetermined quantity of active material calculated to produce thedesired therapeutic effect, in association with a suitablepharmaceutical excipient.

The active compound is effective over a wide dosage range. For examples,dosages per day normally fall within the range of about 0.01 to about 30mg/kg of body weight. A typical daily dose will contain from about 0.01mg/kg to about 100 mg/kg of the active compound of this invention.Preferably, daily doses will be about 0.05 mg/kg to about 50 mg/kg, morepreferably from about 0.1 mg/kg to about 25 mg/kg. In the treatment ofadult humans, the range of about 0.1 to about 15 mg/kg/day, in single ordivided dose, is especially preferred. However, it will be understoodthat the amount of the compound actually administered will be determinedby a physician, in the light of the relevant circumstances, includingthe condition to be treated, the chosen route of administration, theactual compound administered, the age, weight, and response of theindividual patient, and the severity of the patient's symptoms, andtherefore the above dosage ranges are not intended to limit the scope ofthe invention in any way. In some instances dosage levels below thelower limit of the aforesaid range may be more than adequate, while inother cases still larger doses may be employed without causing anyharmful side effect, provided that such larger doses are first dividedinto several smaller doses for administration throughout the day.

The compositions are preferably formulated in a unit dosage form, eachdosage containing from about 5 mg to about 500 mg, more preferably about25 mg to about 300 mg of the active ingredient. The term “unit dosageform” refers to a physically discrete unit suitable as unitary dosagesfor human subjects and other mammals, each unit containing apredetermined quantity of active material calculated to produce thedesired therapeutic effect, in association with a suitablepharmaceutical carrier, diluent, or excipient. The following formulationexamples are illustrative only and are not intended to limit the scopeof the invention in any way.

Formulation 1

Hard gelatin capsules are prepared using the following ingredients:Quantity (mg/capsule) Active Ingredient 250 Starch, dried 200 Magnesiumstearate 10 Total 460

The above ingredients are mixed and filled into hard gelatin capsules in460 mg quantities.

Formulation 2

A tablet is prepared using the ingredients below: Quantity (mg/tablet)Active Ingredient 250 Cellulose, microcrystalline 400 Silicon dioxide,fumed 10 Stearic acid 5 Total 665

The components are blended and compressed to form tablets each weighing665 mg.

Formulation 3

An aerosol solution is prepared containing the following components:Weight % Active Ingredient 0.25 Ethanol 29.75 Propellant 22 70.00(Chlorodifluoromethane) Total 100

The active compound is mixed with ethanol and the mixture added to aportion of the Propellant 22, cooled to −30° C. and transferred to afilling device. The required amount is then fed to a stainless steelcontainer and diluted with the remainder of the propellant. The valveunits are then fitted to the container.

Formulation 4

Tablets each containing 60 mg of active ingredient are made as follows:Quantity (mg/tablet) Active Ingredient 60 Starch 45 Microcrystallinecellulose 35 Polyvinylpyrrolidone 4 Sodium carboxymethyl starch 4.5Magnesium stearate 0.5 Talc 1.0 Total 150

The active ingredient, starch, and cellulose are passed through a No. 45mesh U.S. sieve and mixed thoroughly. The solution ofpolyvinylpyrrolidone is mixed with the resultant powders that are thenpassed through a No. 14 mesh U.S. sieve. The granules so produced aredried at 50° C. and passed through a No. 18 mesh U.S. sieve. The sodiumcarboxymethyl starch, magnesium stearate, and talc, previously passedthrough a No. 60 mesh U.S. sieve, are then added to the granules which,after mixing, are compressed on a tablet machine to yield tablets eachweighing 150 mg.

Formulation 5

Capsules each containing 80 mg medicament are made as follows: Quantity(mg/capsule) Active Ingredient 80 Starch 59 Microcrystalline cellulose59 Magnesium stearate 2 Total 200

The active ingredient, cellulose, starch, and magnesium stearate areblended, passed through a No. 45 sieve, and filled into hard gelatincapsules in 200 mg quantities.

Formulation 6

Suppositories each containing 225 mg of active ingredient may be made asfollows: Quantity (mg/suppository) Active Ingredient 225 Saturated fattyacid glycerides 2000 Total 2225

The active ingredient is passed through a No. 60 mesh U.S. sieve andsuspended in the saturated fatty acid glycerides previously melted usingthe minimum heat necessary. The mixture is then poured into asuppository mold of nominal 2 g capacity and allowed to cool.

Formulation 7

Suspensions each containing 50 mg of medicament per 5 mL dose are madeas follows: Active Ingredient 50 mg Sodium carboxylmethyl cellulose 50mg Syrup 1.25 mL Benzoic acid solution 0.10 mL Flavour q.v. Color q.v.Purified water to total 5 mL

The medicament is passed through a No. 45 mesh U.S. sieve and mixed withthe sodium carboxymethyl cellulose and syrup to form a smooth paste. Thebenzoic acid solution, flavor and color are diluted with some of thewater and added, with stirring. Sufficient water is then added toproduce the required volume.

Formulation 8

An intravenous formulation may be prepared as follows: Quantity ActiveIngredient 100 mg Mannitol 100 mg 5 N Sodium hydroxide 200 mL Purifiedwater to total 5 mLFormulation 9

A topical formulation may be prepared as follows: Quantity ActiveIngredient 1-10 g Emulsifying Wax 30 g Liquid Paraffin 20 g White softparaffin to 100 g

The white soft paraffin is heated until molten. The liquid paraffin andemulsifying wax are incorporated and stirred until dissolved. The activeingredient is added and stirring is continued until dispersed. Themixture is then cooled until solid.

Formulation 10

Sublingual or buccal tablets, each containing 10 mg of activeingredient, may be prepared as follows: Quantity (mg/tablet) ActiveIngredient 10.0 Glycerol 210.5 Water 143.0 Sodium Citrate 4.5 PolyvinylAlcohol 26.5 Polyvinylpyrrolidone 15.5 Total 410.0

The glycerol, water, sodium citrate, polyvinyl alcohol, andpolyvinylpyrrolidone are admixed together by continuous stirring andmaintaining the temperature at about 90° C. When the polymers have goneinto solution, the solution is cooled to about 50°-55° C. and themedicament is slowly admixed. The homogenous mixture is poured intoforms made of an inert material to produce a drug-containing diffusionmatrix having a thickness of about 2-4 mm. This diffusion matrix is thencut to form individual tablets having the appropriate size.

Another preferred formulation employed in the methods of the presentinvention employs transdermal delivery devices (“patches”). Suchtransdermal patches may be used to provide continuous or discontinuousinfusion of the compounds of the present invention in controlledamounts.

The construction and use of transdermal patches for the delivery ofpharmaceutical agents is well known in the art (see, for example, U.S.Pat. No. 5,023,252, issued Jun. 11, 1991) herein incorporated byreference. Such patches may be constructed for continuous, pulsatile, oron demand delivery of pharmaceutical agents.

Frequently, it will be desirable or necessary to introduce thepharmaceutical composition to the brain, either directly or indirectly.Direct techniques usually involve placement of a drug delivery catheterinto the host's ventricular system to bypass the blood-brain barrier.One such implantable delivery system, used for the transport ofbiological factors to specific anatomical regions of the body, isdescribed in U.S. Pat. No. 5,011,472, issued Apr. 30, 1991, which isherein incorporated by reference.

Indirect techniques, which are generally preferred, usually involveformulating the compositions to provide for drug latentiation by theconversion of hydrophilic drugs into lipid-soluble drugs- or prodrugs.Latentiation is generally achieved through blocking of the hydroxy,carbonyl, sulfate, and primary amine groups present on the drug torender the drug more lipid soluble and amenable to transportation acrossthe blood-brain barrier. Alternatively, the delivery of hydrophilicdrugs may be enhanced by intra-arterial infusion of hypertonic solutionsthat can transiently open the blood-brain barrier.

EXAMPLES

The following Examples illustrate the invention. The followingabbreviations are used in the Examples: EtOAc, ethyl acetate; THF,tetrahydrofuran; EtOH, ethanol; TLC, thin layer chromatography, GC, gaschromatography; HPLC, high pressure liquid chromatography, m-CPBA,m-chloroperbenzoic acid; Et₂O, diethyl ether; DMSO, dimethyl sulfoxide;DBU, 1,8-diazabicyclo-[5.4.0]undec-7-ene, MTBE, methyl t-butyl ether;FDMS, field desorption mass spectrometry and r.t., room temperature.

Example 1 Synthesis of Cubanylglycinates IGT 1.0 series

Preparation 1: 4-methoxycarbonylcubane-1-acetyl ethylcarboxylate.

n-butyl lithium (34.83 mmol, 23.5 mL of 1.5 M) is added dropwise to astirred solution of ethyl hydrogen malonate (2.32 g, 17.41 mmol) in 80mL of dry THF under N₂ at −78° C. The mixture was warmed to −30° C. over0.5 h and then re-cooled to −78° C. The acid chloride of cubanemonomethyl ester from example (2) above (2.35 g, 10.46 mmol) in 7 mL ofTHF is added dropwise to the stirred solution. The reaction is warmedslowly to r.t and stirred for a further 1 h. The solution is poured into50 mL of 1 N HCl and extracted with 3×50 mL of diethyl ether. Thecombined organic extracts are further extracted with 20 mL of saturatedsodium hydrogen carbonate and brine, dried over magnesium sulphate,filtered and evaporated to give crude (2). The product is purified bycolumn chromatography on silica with hexanes:ethyl acetate 2:1 to yield.2.5 g (86%) of (2). ¹H NMR (CDCl₃) δ 1.2 (t, 3H) 3.4 (s, 2H), 3.65 (s,3H), 4.2 (m, 8H).

Preparation 2: 4-methoxycarbonylcubane-1-(thioxanthenyl)-acetylethylcarboxylate.

Cubane-β-ketoester (2) (1.15 g, 4.16 mmol) and thioxanthene-9-ol (0.88g, 4.1 mmol) are dissolved in 18 mL of a 1:1 mixture of ethanol:aceticacid and stirred at r.t. for 3 days. The resulting crystalline solid wasfiltered off to yield 1.52 g (77%) of pure (3) m.p. 147-149° C. ¹H NMR(CDCl₃) 1.00 (t, 3H), 3.24 (s, 3H), 3.75 (m, 3H), 3.9 (q, 2H), 4.0 (m,3H, 4.6 (d, 1H), 5.0 (d, 1H), 7.3 (m, 8H).

Preparation 3: 4-carboxycubane-1-methylthioxanthenylketone

The thioxanthenylcubane adduct (3) (1.69 g, 3.57 mmol) is dissolved inethanol 33 mL and 8.7 mL of 1 N NaOH and heated at 70° C. for 4 h. Theresulting solution is evaporated and redissolved in 25 mL of water,acidified with 6 N HCl and extracted with 3×50 mL of diethyl ether. Thecombined organic layers are dried over magnesium sulphate, filtered andconcentrated to give a crude product containing (4). Chromatography onsilica using ethyl acetate gives 1.26 g (88%) of (4)

¹H NMR (CDCl₃) δ 2.8 (d, 2H), 3.8 (m, 3H), 4.0 (m, 3H), 4.7 (t, 1H), 7.3(m, 8H), 9.5 (br, 1H).

Preparation 4: 4-carboxycubane-1-thioxanthenyl-1-(5,5′-hydantoin)

The thioxanthenyl cubane ketone (4) (1.24 g, 3.22 mmol) is dissolved in1:1 ethanol:water (20 mL). Potassium cyanide (0.522 g, 8.0 mmol) andammonium carbonate (1.39 g, 14.4 mmol) are added and the solution heatedin a sealed tube at 85° C. for 65 h. The reaction is cooled andacidified with 2 N HCl and extracted with 3×40 mL of ethyl acetate. Theorganic layers are combined, dried over magnesium sulphate, filtered andevaporated to give (5) 1.3 g (88%) as a crude product. This material washydrolyzed in the next step without purification.

¹H NMR (CD₃OD) δ 1.1 (m, 1H), 2.7 (m, 1H), 3.8 (m, 3H), 4.0 (m, 3H), 4.3(m, 1H), 7.4 (m, 8H).

Preparation 5: 4-carboxycubane-1-thioxanthenyl-1-glycine

The hydantoin adduct (5) (300 mg, 0.65 mmol) is taken up in 1 N NaOH (10mL) and heated at 170° C. for 20 h in a sealed tube. The mixture iscooled and the pH adjusted with 6 N HCl to between 7 and 8. Theprecipitate formed is filtered and washed with water. The combinedfiltrate and washings are combined and evaporated to dryness. Theresulting residue is purified by column chromatography and finally byreverse phase chromatography to yield (6) as colorless crystals. 70 mg.¹H NMR (CD₃OD+D₂O) δ 2.3 (m, 2H), 3.9 (s, 6H), 4.4 (m, 1H), 7.4 (m, 8H).

Example 2

Preparation 1: 4-methoxycarbonylcubane carboxylic acid

A solution of cubane dimethyl ester (6.0 g, 27.24 mmol) in 182 mL of dryTHF is stirred under N₂ at room temperature. A solution of methanolicNaOH (26.7 mmol, 10.7 mL 2.5 M) is added dropwise from a pressureequalized addition funnel and the resulting solution stirred at roomtemperature for 16 h. The mixture is evaporated under reduced pressureat r.t., the residue is taken up in 66 mL of water and extracted with3×25 mL of chloroform. The aqueous layer is acidified to pH 3 withconcentrated HCl and extracted with 3×30 mL of chloroform. The combinedorganic layers were dried over magnesium sulphate, filtered andevaporated to give (8) 182-183° C.: ¹H NMR (CDCl₃) δ 3.72 (s, 3H), 4.27(m, 6H).

Yield 5.1 g (91%).

Preparation 2: 4-methoxycarbonyl-1-(hydroxymethyl) cubane

The mono acid (8) (0.48 g) is dissolved in dry THF (5 mL) and cooled to−70° C. A solution of BH₃ in THF is added slowly with stirring. Thereaction mixture is stirred at −78° C. for 4 hrs and allowed to come toroom temperature. Water (3 mL) is added and stirred for 30 min,potassium carbonate (0.85 g) is added and the solution extracted withEt₂O. The organic phase is dried over magnesium sulfate and evaporatedto give the alcohol (9) 0.46 g (100%) m.p. 83-85° C. ¹H NMR(200 MHz,solvent) δ: 1.58 (s, 1H), 3.62 (s, 3H), 3.72 (s, 2H), 3.81 (m, 3H), 4.1(m, 3H).

Preparation 3: 4-methoxycarbonyl-1-(formyl) cubane

DMSO (0.7 mL, 9.68 mmol) is added to oxalyl chloride (0.42 mL, 4.84mmol) in 12 mL of CH₂Cl₂ at −78° C. The alcohol (9) (0.46 g, 2.42 mmol)in 3 mL CH₂Cl₂ is added and stirred at −78° C. for 1.5 h. Triethylamine(2.0 mL, 14.4 mmol) is added and the mixture is allowed to come to 0° C.Saturated ammonium chloride solution is added and the phases separated,the aqueous layer is extracted with CH₂Cl₂ and the combined organiclayers are dried (MgSO₄), then evaporated to give crude product which ispurified by flash chromatography (1:1 hexanes:diethyl ether) to give0.35 g (76%) of pure product (10). ¹H NMR (200 MHz, solvent) δ: 3.7 (s,3H), 4.2 (m, 3H), 4.32 (m, 3H), 9.72 (s, 1H).

Preparation 4:4-methoxycarbony-1-[2′-hydroxy-1′-phenylethyl]methylnitrilecubane

(R)-phenylglycinol (257 mg, 1.87 mmol) is added to a solution of thealdehyde (10) (0.35 g, 1.84 mmol) in 14 mL of methanol. The solution iscooled to 0° C. and TMSCN (0.49 mL, 3.68 mmol) is added and the mixturestirred at 0° C. overnight. Evaporation of the solvent leaves a residuewhich is purified by chromatography (diethyl ether:hexanes, 3:1) to give0.48 g (77%) of pure product (11). ¹H NMR (CDCl₃) δ: 2.23 (s, 1H), 2.6(br, 1H), 3.5-3.75 (m, 2H), 3.7 (s, 3H), 3.9 (m, 3H), 4.11 (dd, 1H), 4.2(m, 3H), 7.3 (s, 5H).

Preparation 5: 4-carboxy-1-cubanylglycine

Lead acetate (0.69 g, 1.57 mmol) is added to a stirred solution ofnitrile (11) (0.48 g, 1.42 mmol) in dry methanol/dichloromethane 1:1 (12mL). After 10 min 10 mL of water is added and the suspension filteredthrough celite. The organic layer is dried and evaporated to give thecrude imine. The crude imine is refluxed with 6N HCl (30 mL) for 6 hr.The solution is evaporated to dryness and placed on anion exchangeresin, eluting with IN acetic acid to yield the product (12). mp. 241°C. (dec.) ¹H NMR (D₂O) δ 3.96 (s, 1H), 4.01 (m, 3H), 4.14 (m, 3H).

Example 3

Preparation 1: 4-methoxycarbonylcubane carboxylic acid

A solution of cubane dimethyl ester (6.0 g, 27.24 mmol) in 182 mL of dryTHF is stirred under N₂ at r.t. a solution of methanolic NaOH (26.7mmol, 10.7 mL 2.5 M) is added dropwise from a pressure equalizedaddition funnel and the resulting solution stirred at r.t. for 16 h. Themixture is evaporated under reduced pressure at r.t., the residue istaken up in 66 mL of water and extracted with 3×25 mL of chloroform. Theaqueous layer is acidified to pH 3 with concentrated HCl and extractedwith 3×30 mL of chloroform. The combined organic layers were dried overmagnesium sulphate, filtered and evaporated to give (8) 182-183° C.: ¹HNMR (CDCl₃) δ 3.72 (s, 3H), 4.27 (m, 6H). Yield 5.1 g (91%).

Preparation 2: 4-methoxycarbonylcubane-1-carbonyl chloride

The monomethyl ester (8) (1.37 g, 6.65 mmol) is dissolved in 15 mL ofthionyl chloride and gently refluxed overnight. The thionyl chloride isevaporated off and the resultant residue containing (13) was usedimmediately without further purification.

Preparation 3: 4-methoxycarbonylcubane-1-methyl ketone

A suspension of copper iodide (1.49 g, 7.83 mmol) in 30 mL of dry THF isstirred at 0° C. Methyl lithium (15.75 mmol, 11.2 mL of 1.4 M) was addedand stirred at 0° C. for 30 min, then cooled to −78° C. A solution of1.6 g, 7.12 mmol of (13) in 10 mL dry THF is added and the resultantmixture stirred for 1 h. at −78° C. The mixture was quenched withsaturated ammonium chloride solution (15 mL) and extracted with 3×30 mLof diethyl ether. The combined organic layers were dried over magnesiumsulphate, filtered and evaporated to give crude (14). The product waspurified by silica chromatography (hexanes:ethyl acetate, 2: 1) to give1.0 g of product (yield 69%). m.p. 87-89° C.

¹H NMR (CDCl₃) δ 2.17 (s, 3 μl), 3.7 (s, 3H), 4.21 (m, 6H).

Preparation 4: 4-methoxycarbonylcubane-1-methyl-1-(5,5′-hydantoin)

A solution of the methyl ketone (14) (1.0 g, 4.9 mmol) in 40 mL ofethanol and 5.8 mL of 1 N NaOH, is stirred at 70° C. for 4 h. Theresulting solution is evaporated to dryness under reduced pressure andredissolved in 1:1 ethanol: water (20 mL). To this solution is addedpotassium cyanide (0.35 g, 5.4 mmol) and ammonium carbonate (0.96 g, 9.8mmol) and the mixture heated in a sealed tube at 85° C. for 24 h. Thereaction is cooled, acidified with 6 N HCl and reduced in volume until aprecipitate forms. The precipitate is filtered and the filtrateevaporated to dryness and extracted with ethyl acetate. The solvent isevaporated and the product combined with the residue from above to give(15) as a white solid. Yield 0.95 g (75%) m.p. 244-248° C. NMR ₁H (DMSO)δ 1.18 (s, 3H) 3.9 (m, 3H), 4.0 (m, 3H), 8.1 (s, 1H), 10.6 (s, 1H).

Preparation 5: 4-carboxycubane-1-methylglycine

The hydantoin (15) (0.95 g, 3.65 mmol) is dissolved in 30 mL of 2 N NaOHand heated to 170° C. in a sealed tube for 20 h. The reaction is cooledand filtered to remove precipitate and the filter cake washed with 3×10mL of water. The combined aqueous washings are evaporated to give crude(6) which is applied to Spectrum 1×4 anion exchange resin, eluted with0.5 N acetic acid. Isolation by evaporation and crystallization gives(16) as colorless crystals. m.p. >250° C. (decomp.). NMR. ¹H (D₂O) δ1.38 (s, 3H), 3.95 (s, 6H).

Example 4

Experimental Results

Example 1 Compounds of the Present Invention Modulate mGluR Activity

The Chinese hamster ovary cell lines expressing mGluR_(1α), mGluR₂ andmGluR_(4a) receptors have been described previously (Aramori andNakanishi, Neuron 8, 757-765; 1992; Tanabe et al., Neuron 8, 169-179,1992; Tanabe et al., J. Neurosci. 13, 1372-1378). They were maintainedat 37° C. in a humidified 5% CO₂ incubator in Dulbecco's Modified EagleMedium (DMEM) containing a reduced concentration of (S)-glutamine (2 mM)and were supplemented with 1% proline, penicillin (100 U/ml),streptomycin (100 mg/ml) and 10% dialyzed fetal calf serum (all GIBCO,Paisley). Two days before assay 1.8×10⁶ cells were divided into thewells of 24 well plates.

PI hydrolysis was measured as described previously (Hayashi et al., Br.J. Pharmacol. 107, 539-543, 1992; Hayashi et al., J. Neurosci. 14,3370-3377, 1994). Briefly, the cells were labeled with [³H]inositol (2μCi/ml) 24 h prior to the assay. For agonist assays, the cells wereincubated with ligand dissolved in phosphate-buffered saline (PBS)-LiClfor 20 min, and agonist activity was determined by measurement of thelevel of ³H-labeled mono-, bis- and tris-inositol phosphates byion-exchange chromatography. For antagonist assays, the cells werepreincubated with the ligand dissolved in PBS-LiCl for 20 min prior toincubation with ligand and 10 μM (L)-Glutamic acid for 20 min. Theantagonist activity was then determined as the inhibitory effect of the(L)-Glutamic acid-mediated response. The assay of cyclic AMP formationwas performed as described previously (Hayashi et al., Br. J. Pharmacol.107, 539-543, 1992; Hayashi et al., J. Neurosci. 14, 3370-3377, 1994).Briefly, the cells were incubated for 10 min in PBS containing theligand and 10 μM forskolin and 1 mM 3-Isobutyl-1-methyxanthine (IBMX;both Sigma, St. Louis, Mo., USA). The agonist activity was thendetermined as the inhibitory effect of the forskolin-induced cyclic AMPformation. For antagonist assay, the cells were preincubated with liganddissolved in PBS containing 1 mM IBMX for 20 min prior to a 10 minincubation in PBS containing the ligand, 20 μM (mGluR₂) or 50 μM(mGluR_(4a)), (L)-Glutamic acid, 10 μM Forskolin and 1 mM IBMX.

Some of the compounds of the invention were tested for antagonistactivity against Chinese hamster ovary cell lines expressing mGluR_(1α),mGluR₂ and mGluR_(4a) cloned mGluRs at a concentration of 1 mM. Whentested as antagonists of the increase in PI hydrolysis evoked by 10 μM(L)-Glutamic acid, some compounds of the invention effectively blockedthis increase in PI hydrolysis by an action at the mGluR_(1α) receptor.

Example 2 Thioxanthenyl Cubane Inhibits Anoxia Induced Neuronal CellDeath

The neuroprotective effects of a thioxanthenyl cubane (Compound 6) wereexamined using an in vitro anoxia study. Cultured hippocampal pyramindalneurons were exposed to anoxic conditions (oxygen free buffer) for 30minutes. Twenty-four hours post anoxic exposure cell counts wereconducted manually. As shown in FIG. 1, the number of living cells was 2to 3 times greater in anoxic cultures in the presence of Compound 6 thanin control anoxic cultures, suggesting thioxanthenyl cubane inhibitsanoxia induced neuronal cell death and is neuroprotective.

Example 3 Neuroprotective Effects of Thioxanthenyl Cubane in the RatGlobal Ischemia Model

The neuroprotective effects of a thioxanthenyl cubane (Compound 6) wereexamined in vivo using the rat global ischemia model. Briefly, two ofthe four cerebral arteries are permanently occluded and surgical silk isloosely placed around the remaining two cerebral arteries. Temporarytightening of the surgical silk leads to 4 vessel occlusion andtemporary global ischemia. Seven days post ischemic insult, the brain isremoved and the CA1 region of the hippocampus, a region very suspectibleto ischemic damage, is examined.

Intra-peritoneal administration of 1 mg/kg of Compound 6 post ischemicinsult resulted in a greater than 50% reduction in cell death observed 7days after the procedure. As shown in FIG. 2, a reduction in ischemicdamage to the CA1 region of the hippocampus (boxed region) was observedin Compound 6 treated ischemic animals as compared to untreated ischemicanimals. The dark line of cells (viable cells) present in the CA1 regionof the hippocampus of sham operated animals is markedly diminished inischemia alone treated animals. Dramatic improvement in the darkness ofthe band and thus in the number of cells surviving is observed in theCA1 region of ischemic animals treated with Compound 6 as compared tocontrol ischemic animals. The results therefore demonstrate theneuroprotective properties of Compound 6.

Example 4 Neuroprotective Effects of Thioxanthenyl Cubane in a FocalIschemia Model

The neuroprotective effects of a thioxanthenyl cubane (Compound 6) werefurther examined using a starch microsphere infusion focal ischemiamodel. Briefly, starch microspheres are injected unilaterally into oneof the carotid arteries. Blood flow is temporarily occluded on theinjected side for approximately 30 minutes. Reperfusion occurs after theinitial starch clot is resolved.

Compound 6 was intra-peritoneally administered at dosages of 0.1, 1.0,and 10 mg/kg either prophylactically or therapeutically. Theprophylactic dose schedule included a dose of Compound 6 administered 30minutes prior to ischemic insult followed by doses at 30 minutes and 3hours post insult. For therapeutic administration, Compound 6 wasadministered 3 hours post insult only. As shown in FIGS. 3 a and b, areduction in ischemic damage to the hippocampus, especially in theretrospenial and piriform cortices, was observed in Compound 6 treatedischemic animals as compared to untreated ischemic animals (results weresimilar for both Compound 6 treatment schedules). Dramatic increase inthe darkness of the cell bands and thus in the number of cells survivingwas observed in the hippocampus, especially in the retrospenial andpiriform cortices, of ischemic animals treated with Compound 6 ascompared to control ischemic animals. Neuroprotection was observed inall animals treated with Compound 6 and no obvious dose dependence wasnoted. As shown in FIGS. 3 c and d there was no significant differencein neuronal cell number between the ipsilateral and contralateral sidesof the CA1 region in either the prophylactic or therapeutic treatmentgroups. In contrast, significant differences were observed in controltreated animals. In addition to providing substantial neuroprotection,Compound 6 reduced the incidence of seizures following ischemic insultin a dose-dependent manner. The results therefore demonstrate thatCompound 6 protects neurons from ischemic damage at relatively lowdoses.

Example 5 The Anxiolytic Properties of Thioxanthenyl Cubane (FearPotentiated Startle Model)

The anxiolytic properties of a thioxanthenyl cubane (Compound 6) wereexamined using the fear potentiated startle model. This model permitsmeasurement of learned fear of a stimulus that has been paired withrepeated foot shocks. The effect of Compound 6 on fear potentiatedstartle was compared with the known standard, diazepam. All tests wererun 30 min after intraperitoneal drug administration. Compound 6 wasadministered at 1.0, 3.0, 10 and 15 mg/kg in rats. As shown in FIG. 4,compared to diazepam at 3 mg/kg, Compound 6 showed a dose dependentreduction in fear potentiated startle with an apparent maximum at 3mg/kg. The highest dose showed a tendency to reverse the effect.

Example 6 The Anxiolytic Properties of Thioxanthenyl Cubane (FearInduced Freezing Model)

The anxiolytic properties of a thioxanthenyl cubane (Compound 6) werealso examined using the fear induced freezing model. Briefly, this testrelies on the induction of a well known effect in rats when they arechallenged. The rat is subjected to a mild shock associated with a soundwhich results in the animal becoming very still when expecting thatshock.

The animal is placed in its home cage for acclimatization before beingplaced back in the test environment in the presence or absence of testcompound. The reduction in freezing is used as a measure of anxiolysis.The behavior was observed in the environment alone (context alone) orenvironment with the conditioning sound (context plus tone). The secondparadigm (context plus tone) produces a larger and more difficult toovercome anxiety. As shown in FIG. 5, Compound 6 was effective in bothscenarios compared to diazepam at 3 mg/kg, which is only effective inthe less stringent first paradigm (context alone).

Example 7 The Anxiolytic Properties of Thioxanthenyl Cubane (SocialInteraction Studies)

The effect of a thioxanthenyl cubane (Compound 6) on social interactionwas examined in rodents. Briefly, social interaction is measured asfollows: a strange intruder is introduced into the cage of anacclimatized treated rat and the number of times the rat either bites (#bites) or wrestles (# pins) the intruder is determined. Compound 6 wasadministered at three doses and compared to saline and diazepam at 2mg/kg. As shown in FIG. 6, Diazepam shows a clear reduction in bites andpins at 2 mg/kg and Compound 6 compares well, giving an equal reductionat 10 mg/kg in both bites and pins.

Example 8 The Anxiolytic Properties of Thioxanthenyl Cubane (ElevatedPlus Maze)

To further examine the anxiolytic properties of a thioxanthenyl cubane(Compound 6), the elevated plus maze test was conducted. The elevatedplus maze test is sensitive to benzodiazepine type anxiolytics whileother anxiolytics such as the serotonin reuptake inhibitors (SSRIs) showpoor efficacy in this test. This test is dependent on the predispositionof rodents to remain in the dark and offers the choice between darkareas of the maze and the opportunity to explore lighted areas. As shownin FIG. 7, diazepam at 2 mg/kg shows a clear increase in the time thatthe rat spends in the exposed area of the maze. In contrast, Compound 6shows only a tendency of the rat to occupy the light area of the maze at1 mg/kg, therefore indicating that the mechanism of action of Compound 6is different to that of the benzodiazepines.

Example 9 Oral Bioavailability/Efficacy of Thioxanthenyl Cubane

The oral bioavailability and efficacy of a thioxanthenyl cubane(Compound 6) was studied using the fear potentiated startle model.Compound 6 was administered by gavage at a dose of 12 mg/kg. Following a90 minute period allowed for drug absorption, the oral efficacy wasexamined using the fear potentiated startle model. As shown in FIG. 8oral Compound 6 was effective in reducing the fear potentiated startlemodel. The Compound 6 was found to be effective at a dose level between7 and 15 mg/kg when compared to an effective dose of 7 mg/kg diazepam(FIG. 9).

Example 10 Onset and duration of Action of Thioxanthenyl Cubane

The onset and duration of a thioxanthenyl cubane (Compound 6) wasstudied using the fear potentiated startle model. Thioxanthenyl cubanewas administered by gavage at a dose of 15 mg/kg. The effect of oralCompound 6 on fear potentiated startle was examined at 30 minutes, 1, 2,4, 6 and 8 hours post drug administration. The results are summarized inFIG. 10 and demonstrate that Compound 6 begins to have an effect early,at 30 minutes and that effect seems to grow to a maximum at 4 hours andbegins to wane sometime after that, back to base line at 8 hours.

Example 11 Side Effect Profile for Thioxanthenyl Cubane

The side effect profile for an intra-peritoneally administeredthioxanthenyl cubane (Compound 6) was examined and compared to diazepamusing functional observational battery which is a series ofobservational markers designed to indicate level of impairment. Thegreater the functional observational battery score, the greater theimpairment. As shown in FIG. 11, a large degree of impairment wasobserved in animals treated with high doses of diazepam, however thislevel of impairment was not observed with very high doses of Compound 6.

To further examine the side effect of profile of Compound 6 theassymmetric grid test was conducted to measure impairment of motorfunction. Briefly, in the assymetric grid test the animal is placed onone side of a grid pattern, designed to challenge the animals motorfunction. On the other side of the grid is the animal's home cage or areward. As the animal enters the grid it is monitored for mistakes by acamera placed horizontally in line with the grid. The camera records thenumber of forelimb and hindlimb intrusions through the grid and thehigher the number, the greater the impairment. As shown in FIG. 12,following a dose of 4 mg/kg diazepam, the number of mistakes increasessignificantly compared to the null experiment. Compound 6 administeredat doses up to 10 mg/kg, produced no significant change in either foreor hindlimb mistakes, indicating a total lack of cognitive impairmentcompared to diazepam.

1. A compound of the formula:

or a pharmaceutically acceptable salts or hydrates thereof, or apharmaceutically acceptable metabolically-labile ester or amide thereof,wherein: R1 is an acidic group selected from the group of carboxyl,phosphono, phosphino, sulfono, sulfino, borono, tetrazol, isoxazol,—CH₂-carboxyl, —CH₂-phosphono, —CH₂-phosphino, —CH₂-sulfono,—CH₂-sulfino, —CH₂-borono, —CH₂-tetrazol, and —CH₂-isoxazol; R2 is abasic group selected from the group of 1° amino, 2° amino, 3° amino,quaternary ammonium salts, imidazol, guanidino, boronoamino, allyl-urea,thiourea, and NHR5, wherein R5 is —H or an acyl group; R3 is of theformula;

wherein: Y is absent or selected from the group of (CH₂)_(n) (wheren=1-4), C═O, O, or NH; X is selected from the group of O, NH, S, S═O, orSO₂; R_(a), R_(b), R_(c), R_(d), R_(c), R_(f), R_(g) and R_(h) areindependently selected from the group of —H, hydroxyl, lower alkyl,substituted lower alkyl, lower alkoxy, alkenyl, alkynyl, amino, halogen,aryl, substituted aryl, nitrile, acyl, carboxy or am ido; R4 is a groupselected from the group of carboxyl, phosphono, phosphino, sulfono,sulfino, borono, tetrazol, isoxazol; with the proviso that, when X═S andY is absent or (CH₂)_(n) then at least one of R_(a) through R_(h) isother than —H.
 2. The compound as claimed in claim 1, wherein R1 is COOHor —CH₂COOH.
 3. The compound as claimed in claim 1, wherein R2 is NH₂.4. A pharmaceutical formulation, which comprises the compound accordingto claim 1, and a pharmaceutically acceptable carrier, diluent orexcipient.
 5. Use of the compound according to claim 1, to modulate oneor more metabotropic glutamate receptor (mGluR) functions in a warmblooded mammal.
 6. Use of the compound according to claim 1, toantagonize mGluRs group I, or agonize mGluRs group II, or agonize mGluRsgroup III in a mammal in need thereof.
 7. Use of the compound accordingto claim 1 for the treatment of a neurological disease or disorderselected from the group of: cerebral deficits subsequent to cardiacbypass surgery and grafting, cerebral ischemia, stroke, cardiac arrest,spinal cord trauma, head trauma, perinatal hypoxia, and hypoglycemicneuronal damage, Alzheimer's disease, Huntington's Chorea, amyotrophiclateral sclerosis, AIDS-induced dementia, ocular damage, retinopathy,cognitive disorders, idiopathic and drug-induced Parkinson's disease,muscular spasms, convulsions, migraine headaches, urinary incontinence,psychosis, drug tolerance, withdrawal, and cessation (i.e. opiates,benzodiazepines, nicotine, cocaine, or ethanol), smoking cessation,anxiety and related disorders (e.g. panic attack), emesis, brain edema,chronic pain, sleep disorders, Tourette's syndrome, attention deficitdisorder, and tardive dyskinesia.
 8. Use of the compound according toclaim 1 for the treatment of a psychiatric disease or disorder selectedfrom the group comprising: schizophrenia, anxiety and anxiety relateddisorders, panic attack, depression, bipolar disorders, psychosis, andobsessive compulsive disorders.
 9. Use of the compound according toclaim 1 for the treatment of anoxia induced neuronal cell death,cerebral ischemia, stroke, anxiety and anxiety related disorders,ischemia-related neuropathies from surgical procedures, glaucoma andmacular degeneration or modulation of mGluRs in a mammal in need of suchtherapy.
 10. Use of a prophylactically effective amount of a compound ofthe formula:

or a pharmaceutically acceptable salts or hydrates thereof, or apharmaceutically acceptable metabolically-labile ester or amide thereof,to prevent a disease or condition in a mammal in need thereof, wherein:R1 is an acidic group selected from the group of carboxyl, phosphono,phosphino, sulfono, sulfino, borono, tetrazol, isoxazol, —CH₂-carboxyl,—CH₂-phosphono, —CH₂-phosphino, —CH₂-sulfono, —CH₂-sulfino, —CH₂-borono,—CH₂-tetrazol, and —CH₂-isoxazol; R2 is a basic group selected from thegroup of 1° amino, 2° amino, 3° amino, quaternary ammonium salts,imidazol, guanidino, boronoamino, allyl, urea, thiourea, and NHR5,wherein R5 is —H or an acyl group; R3 is of the formula;

wherein: Y is absent or selected from the group of (CH₂)_(n) (wheren=1-4), C═O, O, or NH; X is selected from the group of O, NH, S, S═O, orSO₂; R_(a), R_(b), R_(c), R_(d), R_(e), R_(f), R_(g) and R_(h) areindependently selected from the group of —H, hydroxyl, lower alkyl,substituted lower alkyl, lower alkoxy, alkenyl, alkynyl, amino, halogen,aryl, substituted aryl, nitrile, acyl, carboxy or amido; R4 is a groupselected from the group of carboxyl, phosphono, phosphino, sulfono,sulfino, borono, tetrazol, isoxazol.
 11. The use according to claim 10,wherein said disease or condition is selected from anoxia induced celldeath, ischemia-related neuropathies from surgical procedures, glaucomaand macular degeneration.
 12. Use of a prophylactically effective amountof a compound of the formula:

or a pharmaceutically acceptable salts or hydrates thereof, or apharmaceutically acceptable metabolically-labile ester or amide thereof,as neuroprotectant in a mammal in need thereof, wherein: R1 is an acidicgroup selected from the group of carboxyl, phosphono, phosphino,sulfono, sulfino, borono, tetrazol, isoxazol, —CH₂-carboxyl,—CH₂-phosphono, —CH₂-phosphino, —CH₂-sulfono, —CH₂-sulfino, —CH₂-borono,—CH₂-tetrazol, and —CH₂-isoxazol; R2 is a basic group selected from thegroup of 1° amino, 2° amino, 3° amino, quaternary ammonium salts,imidazol, guanidino, boronoamino, allyl, urea, thiourea, and NHR5,wherein R5 is —H or an acyl group; R3 is of the formula;

wherein: Y is absent or selected from the group of (CH₂)_(n) (wheren=1-4), C═O, O, or NH; X is selected from the group of O, NH, S, S═O, orSO₂; R_(a), R_(b), R_(c), R_(d), R_(e), R_(f), R_(g) and R_(h) areindependently selected from the group of —H, hydroxyl, lower alkyl,substituted lower alkyl, lower alkoxy, alkenyl, alkynyl, amino, halogen,aryl, substituted aryl, nitrile, acyl, carboxy or amido; R4 is a groupselected from the group of carboxyl, phosphono, phosphino, sulfono,sulfino, borono, tetrazol, isoxazol.
 13. Use of a therapeuticallyeffective amount of a compound having the formula:

or a pharmaceutically acceptable salts or hydrates thereof, or apharmaceutically acceptable metabolically-labile ester or amide thereof,for the treatment of anoxia induced neuronal cell death, cerebralischemia, stroke, anxiety and related disorders, ischemia-relatedneuropathies from surgical procedures, glaucoma and macular degenerationor modulation of mGluRs in a mammal in need of such therapy.
 14. The useaccording to any one of claims 10, 11, or 12, wherein in the saidcompound: Y is (CH₂)_(n) and X is O, NH, S, S═O or SO₂.
 15. The useaccording to any one of claims 10, 11, or 12, wherein in the saidcompound: Y is (CH₂)_(n) and X is O or S, S═O or SO₂.
 16. The useaccording to any one of claims 10, 11, or 12, wherein in the saidcompound: R1 is carboxy or —CH₂-carboxy; R2 is 1° amino, 2° amino, 3°amino; R3 is xanthenyl or thioxanthenyl or —CH₂-xanthenyl or—CH₂-thioxanthenyl R4 is carboxy.
 17. The use according to any one ofclaims 10, 11, or 12, wherein in the said compound: wherein: R1 is COOHor —CH₂—COOH R2 is NH₂ R3 is xanthenyl or thioxanthenyl or—CH₂-xanthenyl or —CH₂-thioxanthenyl R4 is COOH
 18. Use of aprophylactically effective amount of a compound having the formula:

or a pharmaceutically acceptable salts or hydrates thereof, or apharmaceutically acceptable metabolically-labile ester or amide thereof,as a neuroprotectant in a mammal in need of such therapy.
 19. Use of aprophylactically effective amount of a compound having the formula:

or a pharmaceutically acceptable salts or hydrates thereof, or apharmaceutically acceptable metabolically-labile ester or amide thereof,in the prevention of anoxia induced cell death in a mammal in need ofsuch therapy.
 20. Use of a prophylactically effective amount of acompound having the formula:

or a pharmaceutically acceptable salts or hydrates thereof, or apharmaceutically acceptable metabolically-labile ester or amide thereof,to prevent disease or conditions in a mammal in need of such therapy.